A Systematic Review of Water and Gender Interlinkages: Assessing the Intersection With Health

Background: Significant developmental challenges in low-resource settings limit access to sustainable water, sanitation, and hygiene (WASH). However, in addition to reducing human agency and dignity, gendered WASH inequities can also increase disease burden among women and girls. In this systematic review, a range of challenges experienced by women relating to inadequate WASH resources are described and their intersection with health are explored. We further assess the effectiveness of interventions in alleviating inequalities related to the Sustainable Development Goals (SDGs) three (health), five (gender), and six (water). Methods: We searched the MEDLINE database to identify research articles related to water (i.e., WASH), gender, and sustainability. An analysis of both observational and interventional studies was undertaken. For each study, content analysis was performed to identify the relevant WASH, gender, and health related outcomes, and the main conclusions of the study. Results: Key themes from our search included that women and girls face barriers toward accessing basic sanitation and hygiene resources, including a lack of secure and private sanitation and of Menstrual Hygiene Management (MHM) resources. In total, 71% of identified studies reported a health outcome, suggesting an intersection of water and gender with health. Half of the research studies that included a health component reflected on the relationship between WASH, gender, and infantile diseases, including under-5 mortality, waterborne parasites, and stunting. In addition, we found that women and girls, as a result of their role as water purveyors, were at risk of exposure to contaminated water and of sustaining musculoskeletal trauma. A limited number of studies directly compared gender differences in accessing WASH resources, and an even smaller fraction (N = 5, 8.5%) reported sex-disaggregated outcomes. Educational, infrastructural, and programmatic interventions showed promise in reducing WASH and health outcomes. Indeed, infrastructural WASH interventions can be successful if long-term maintenance is ensured. Conclusions: Significant WASH inequities in women and girls further manifest as health burdens, providing strong evidence that the water-gender-nexus intersects with health. Thus, addressing gender and water inequities holds the potential to alleviate disease burden and have a significant impact on achieving the SDGs, including SDG three, five, and six.


INTRODUCTION Rationale
Water is necessary for life, and for numerous derived essential applications ranging from industry, agriculture, drinking, sanitation, and hygiene. The Joint Monitoring Program (JMP) describes how among the least developed countries, 35% lacked access to basic water needs (i.e., water from an improved water source which can be retrieved within a 15 min round trip), 65% lacked access to basic sanitation (i.e., a toilet or latrine which protects against soil leaching by contaminants), and 73% lacked access to basic hygiene (i.e., a handwashing facility with soap and water) (WHO and UNICEF, 2019). These staggering statistics point to a lack of critical human development, especially for the vulnerable and marginalized populations. Recognizing the importance of accessing water, the Sustainable Development Goals (SDGs), as demonstrated by SDG 6 which emphasizes "clean water and sanitation" (targets 6.1 and 6.2), outline indicators for ensuring sustainable and equitable access to water for all. Broadly, these SDG targets focus on providing ubiquitous access to sustainable water, basic sanitation and hygiene (WASH) to redress deficiencies prevalent among low-and middle-income countries (LMICs) and populations living in vulnerable situations .
It is paramount to recognize that inequities in accessing WASH resources are further exacerbated among specific populations. For example, rural populations and women represent marginalized groups who are unduly encumbered by poor WASH practices or face additional challenges in accessing WASH resources (WHO and UNICEF, 2019). Women and girls disproportionately serve as water purveyors, collecting water in eight of 10 households, and as such, often face the burdens of needing to transit long distances to retrieve water (WHO and UNICEF, 2017). Moreover, women and girls require additional resources to address their menstrual hygiene management (MHM) needs. According to the 2017 JMP report (WHO and UNICEF, 2017), MHM is stated as, ". . . using a clean menstrual management material to absorb or collect menstrual blood, that can be changed in privacy as often as necessary for the duration of a menstrual period, using soap and water for washing the body as required, and having access to safe and convenient facilities to dispose of used menstrual management materials." MHM is instrumental in progressing women's and girls' ability to manage their menstrual periods safely and with dignity; thereby, allowing them to participate in school, work, and other activities (Sommer et al., 2016). In general, WASH-related challenges among women are often exacerbated by women's general reduced agency in low-resource settings and need to be appropriately addressed to ensure gender equity objectives.
Despite these gender-related deficiencies, research assessing the intersection between gender and water is severely lacking and remediating gender-water inequities will require targeted resources to fill in the gaps. For example, the 2014 JMP report did not collect sex-disaggregated data, and in 2015, it reported obstacles in collecting sex-disaggregated data (Fletcher and Schonewille, 2015). The 2014 UN-Water Global Analysis and Assessment of Sanitation and Drinking-Water survey also entirely excluded sex-disaggregated data reporting (Fletcher and Schonewille, 2015). In 2019, the World Water Development Report likewise highlights this gap, more specifically related to WASH and MHM related challenges for populations living in vulnerable situations .
There are further interlinkages existing between water, gender, and health-worsening WASH-inequities among women cause associated health burdens. Among other burdens, poor WASH practices elevate the risk for waterborne diseases, including for example cholera, a bacterial infection and transmitted by contaminated water and poor sanitation and hygiene practices (Mahamud et al., 2011;Fletcher and Schonewille, 2015). Given the role of women in water provisioning for households, they are at an increased risk of exposure to transmission and contraction of disease (World Health Organization, 2011). Likewise, urinary tract infections (UTI's) as a result of poor MHM practices, can result in school absences and an overall reduced education (Sommer et al., 2016).
In this way, the SDGs are uniquely interconnected, particularly with respect to accessing water, as the SDG 6 Synthesis Report (2018) reflects-"Water resources are embedded in all forms of development (e.g., food security, health promotion, and poverty reduction), in sustaining economic growth in agriculture, industry and energy generation, and in maintaining healthy ecosystems" (United Nations, 2018). Despite this, a detailed understanding of the interlinkages between water and gender is lacking. Moreover, given that the health burdens associated with poor WASH can disproportionately entangle women, the water-gender interlinkages with health need to be carefully examined and, subsequently, integrated into policies.
One step toward helping fill this gap has been the work completed by United Nations Educational, Scientific and Cultural Organization (UNESCO) in developing the Water and Gender toolkit for collecting sex-disaggregated data in the water sector [World Water Assessment Programme (UNESCO WWAP), 2019]. The updated toolkit introduces a set of new indicators to better elucidate how women and girls experience inequities related to accessing or making decisions regarding water and water-related tasks [World Water Assessment Programme (UNESCO WWAP), 2019]. However, more work is needed to understand the landscape of the water-gender nexus as it has currently been described in the literature, and to interrogate its intersection with health.

Objectives
To survey observational and interventional studies of adults and children conducted globally to identify the range of WASH challenges experienced by women; identify major health burdens associated with lacking WASH provisions, and specifically within women; identify key themes of WASH interventions for addressing burdens associated with the water, gender, and health interlinkages.

Research Question
This research aimed to interrogate the question, do WASH based deficiencies disproportionately burden women? If so, do these deficiencies manifest through augmenting health burdens among women and girls?

Study Design
We conducted a systematic review using a broad-based content analysis through the PRISMA guidelines. This approach was adopted for an investigation that aimed to include key highlights identified by each study with respect to the water-gender interlinkages and its intersection with health.

Participants
For each paper, the population of women was considered and was subdivided into three categories: (1) girl/adolescent, (2) pregnant/maternal women, (3) household/adult women. WASH was categorized with respect to whether it addresses (1) water, (2) sanitation, (3) hygiene, or (4) MHM. Health outcomes were categorized based on the disease or the burden described. For each WASH and health outcome, relevant outcomes relating to poor WASH accessibility, or health were described. Where available, an assessment of whether the study directly compares gender, and whether poor WASH or health outcomes were gender specific was considered. In studies that focused solely on women, whether specific gender-based challenges are identified and documented was also noted.

Search Strategy
A two-phase strategy was adopted to search the literature for documents/papers mining. A comprehensive keyword search of the primary literature was conducted using the MEDLINE database. After excluding irrelevant papers, in phase 2, a broad content analysis was adopted to identify relevant, and broadreaching WASH and health data information. A single search approach was used to first comprehensively identify articles related to the water-gender nexus. Subsequently, these articles were analyzed to determine whether a health component was present. In short, a selection criterion was outlined and adopted to shortlist the papers.

Phase 1: Search Strategy and Aggregation of Data and Information
A systematic review of MEDLINE publications via PubMed was used. Search terms surrounding three categories [gender, water, and sustainability], were incorporated in the search query. For each category, terms spanning multiple dimensions of that theme and derived words were searched. For instance, the search terms for gender included: woman, women, female, sex, gender, girls, girl, gender equality, gender gap, women's empowerment, and women empowerment. In addition, for water: WASH, water sanitation and hygiene, sanitation, clean water, safe water, hygiene, water access, water security, water availability, water collection, water management, fetching water, water fetching, drinking water, water sources, and water source. The search terms for sustainability included: sustainable development goal, sustainable development goals, sustainable development, SDG, SDGs, sustainability, and sustainable.
Our inclusion criteria included observational studies and clinical trials that utilized a quantitative, qualitative, or mixedmethods design; was available in English; contained a WASH outcome; and explicitly considered a gendered outcome (i.e., in women or girls, or gender/sex differences). Exclusion criteria included studies not focused on humans, that did not provide primary data or analysis (i.e., commentaries, systematic reviews, literature reports) and did not consider a population (i.e., case reports). Figure 1 provides a flowchart of the methodological approach.

Phase 2: Criteria Based Analysis
For each of the selected research papers, data were collected describing the study design, location, population, WASH outcomes, health outcomes, whether the study was sex-disaggregated, and the key highlights. For interventional studies, information describing the intervention were examined. Sex-disaggregated data was defined as data whereby indicators for men and women are separately provided.

Assessing Risk of Bias
We assessed the risk for bias in individual studies using a previously validated adaptation of the Cochrane risk of bias instrument (Akl et al., 2012). Bias is assessed based on the response options "definitely yes or no" or "probably yes or no" to criteria highlighted separately for cross-sectional, cohort, and randomized control trials (Supplemental Tables 1-3). Questions include for example, "Is the source population representative of the population of interest?, " where affirmative answers indicate less bias, and negative responses indicating greater bias. Information regarding the risk of bias tools used can be found at https:// www.evidencepartners.com/resources/methodologicalresources.
In brief, cross-sectional studies with low bias are characterized by the demonstrated use of a valid sampling strategy (e.g., simple sampling, cluster sampling, etc.); an adequate participant response/inclusion rate; little reported missing data; the inclusion of relevant outcome measures; and validation of the data collection method (e.g., pilot testing, previously validated approach).
Cohort studies with low bias are characterized by evidence that individual cohorts are drawn from a common underlying population (i.e., similar communities which deviate mainly due to exposure to the factor of interest); use satisfactory data collection modalities for relevant factors, outcomes, and confounds; ensure that baseline levels of the outcome of interest are absent or equally low; ensure minimal differences in other confounding variables, or, use appropriate statistical methods to account for confounds (e.g., matching, or regression); use an appropriate follow-up strategy with a high degree of participant retention; are not impacted by the differential exposure to other interventions/ameliorating strategies (e.g., free education is present in only one community).
Randomized control trials with low bias ensure the random allocation of patients to the respective treatment groups (e.g., simple random stratification, matched stratification); that the randomization procedure is concealed; adequate blinding of participants, healthcare providers, data collectors, outcome assessors, and data analysts; a low loss to follow-up; report all pre-determined outcome measures (e.g., do not selectively withhold results, or statistical analyses); and was generally conducted in a statistically sound, valid, and reliable manner (e.g., use appropriate data collection instruments, have appropriate controls).

Study Selection and Characteristics
This analysis identified 59 research articles from 30 countries published between 1993 and 2019. Close to half of the publications conducted analyses in Sub-Saharan Africa with Kenya (N = 7) and Nigeria (N = 5) representing the most frequently studied countries. Table 1 describes 46 identified observational studies included in the analysis, while Table 2 describes 13 identified interventional studies. Primarily, WASH studies focused on measuring access to water (74%), followed by access to sanitation (54%), hygiene (10%), and MHM (7%). As well, close to half of studies (46%) focused exclusively on the experience of women and girls and did not consider impacts on men. Only five publications (8.5%) reported some sex-disaggregated outcomes.

Synthesized Findings
Women Are the Primary Water Purveyors, Particularly in the Developing Regions of the World Largely, the identified observational studies ( Table 1) emphasized issues in accessing clean water among women and girls, and described that a lack of clean water and water resources negatively contributed to women and girl's health and quality of life (Doherty et al., 2007;Bornman et al., 2012;Sato et al., 2016;Gaspar et al., 2017;Vos et al., 2017;Angoua et al., 2018;Prado et al., 2019). Studies which considered gender likewise revealed a lack of access to improved water for both men and women alike (Ugbomoiko et al., 2009;Al-Delaimy et al., 2014;Atalabi et al., 2016;Holvoet et al., 2016;Akombi et al., 2017;Baker et al., 2018). Few studies directly compared whether access to water differed as a result of a gender. However, Bisung and Elliott (2018) showed that female-headed households had reduced access to water security (Bisung and Elliott, 2018). Moreover, within a household, there was substantial evidence that women as the primary carriers of water with prevalence estimates ranging from 61 to 79% (Hunter, 2006;Bornman et al., 2012;Holvoet et al., 2016;Geere et al., 2018). Indeed, the presence of a wife in the household significantly increased the likelihood of having access to clear water (Angoua et al., 2018). Mean travel times for fetching water were as high as 54 min (Holvoet et al., 2016). Consequently, poor access to water at a household level disproportionately impacts women and girls who are commonly responsible for securing water.

Women Face Unique WASH and MHM Challenges
A multitude of studies focused on women and girls and demonstrated that women practiced poor sanitation, hygiene, and MHM practices, largely due to lacking resources. Sanitation facilities were commonly cited to not be safe, clean, and accessible (Kwiringira et al., 2014;Sato et al., 2016;Khan et al., 2017;Aluko et al., 2018;Angoua et al., 2018;Dendup et al., 2018;Desalegn et al., 2018;Njuguna, 2019;Winter et al., 2019). Basic needs, such as soap and washing facilities, and hygienic products, such as toothpaste were documented as hygiene barriers (Budhathoki et al., 2018;Lubon et al., 2018). Moreover, women and girls often cited that critical challenges No Improved access to drinking water and sanitation correlated with a reduced under-5 mortality rate; female metrics had no effect.

No
After confound adjustment, high-quality water and sanitation had no effect on under-5 mortality. Female education reduced under-5 mortality.
Child stunting Access to an improved water source Compared gender differences.

No
Four in 10 used water from an unimproved source. Male children were more likely to be stunted in comparison to females for both 0-23 months and 0-59 months old. Access to an improved drinking water decreased the odds of stunting by ∼30% in children aged 0-59 months old.

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Frontiers in Water | www.frontiersin.org No 22.7% of students possessed genito-urinal schistosomiasis. Boys were 7-fold more likely to be infected with schistosomiasis. Unclean water was associated with increased infections, as were mothers who were employed as "brown collared workers" or were homemakers.

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Frontiers in Water | www.frontiersin.org No A lack of safe sanitation facilities increased the odds of under-five mortality by 1.5-fold, and access to safe water had no effect. Among gender-related factors, mothers who were older than 25 reduced the risk of under-five mortality by 2-5-fold. Other gender related factors had no effect.

Frequency of underweight mothers
Access to an improved water source, and a household toilet.
Focused on lactating mothers.

No
Fasting mothers without a non-improved water source, or a toilet were 1.6-fold, and 1.5-fold, respectively more likely to be underweight.  Assessed gender differences.

Yes
Female heads/partners (∼40%) and daughters (∼20%) were the primary water carriers. Regardless of the time it took for water fetching, improving water access was prioritized more than improving employment opportunities. Male headed households, and sons traveling >15 min to fetch water were >10-fold more likely to state water access as a more important priority than health services. Girls who traveled <15 min were 8.5-fold more likely to declare employment as an important priority than water access.

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Frontiers in Water | www.frontiersin.org (Continued) Frontiers in Water | www.frontiersin.org included a lack of privacy, conveniently located latrines, as well as locks and security (Kwiringira et al., 2014;O'Reilly and Louis, 2014;Winter et al., 2019). In particular, a lack of privacy and security were related to women emptying bags and buckets at night, a behavior that can often increase the exposure of women to the threat of violence or sexual assault (Winter et al., 2019). Generally, studies that compared access to sanitation between men and women found largely unremarkable gender differences (Ugbomoiko et al., 2009;Al-Delaimy et al., 2014;Alemu et al., 2017;Baker et al., 2018). However, one study in rural Ethiopia found that male-headed households were ∼4-fold more likely to use household latrines than female-headed families (Aiemjoy et al., 2017). In addition, Njuguna (2019) showed that in Kenya, in 2004 and 2008, but not 2014, female-headed households were more likely to openly defecate than male-headed households. There is further evidence that girls had reduced access to improved hygienic practices. Nasr et al. (2013) comment that boys hand washed more frequently than girls, and Oberoi et al. demonstrated that girls less often changed their toothbrush and cited cost as a barrier (Oberoi et al., 2014).
A small fraction (6%) of studies focused on the role of MHM, where women reported a lack of proper MHM products, such as clean pads, in addition to private areas and an absence of water provisioning for cleaning and sanitation needs (Khan et al., 2017;Budhathoki et al., 2018;Davis et al., 2018). Davis et al. (2018) demonstrated how one in 10 students missed school due to menstruation, and this could, in part be attributed to menstrual stigma. However, the link between WASH resources in school and absenteeism was not definitive.

Poor Access to WASH Resources Disproportionately Impacts Health Burdens Among Women and Girls, and Particularly Children
We found significant evidence of gender intersecting with WASH and health, with 33 of the 46 observational studies (72%) assessing a health component in relation to WASH (Figure 2). In total, 16 (48%) studies assessed childhood health and childhood infectious diseases, mainly centering on under-five mortality (15%), schistosomiasis/intestinal parasites (18%), and childstunting (12%). Concretely, studies showed that maternal, or household access to clean water significantly reduced the risk of under-five mortality (Ahmed et al., 2016;Acheampong et al., 2017Acheampong et al., , 2018, child stunting (Akombi et al., 2017;Vos et al., 2017;Marinda et al., 2018), schistosomiasis (Atalabi et al., 2016;Donohue et al., 2017), and hookworm infections (Baker et al., 2018). Household piped water was one of the three stability factors needed to reduce HIV transmission for newborn infants (Doherty et al., 2007). Outside of the home, exposure to open water near schools increases the risk of schistosomiasis (Kapito-Tembo et al., 2009). Other aspects of WASH, including improved sanitation and handwashing, likewise reduced underfive mortality (Ahmed et al., 2016;Dendup et al., 2018), and schistosomiasis (Donohue et al., 2017), or acquiring other soiltransmitted helminths and parasites (Baker et al., 2018). In addition to the availability of sustainable WASH resources, maternal factors contributed to health burdens. Demographic  factors, including the mother's BMI (Marinda et al., 2018;Prado et al., 2019), age (Dendup et al., 2018), education level (Nasr et al., 2013;Hasan and Richardson, 2017;Akachi et al., 2018;Prado et al., 2019), and lack of employment (Atalabi et al., 2016) were all found to increase the risk of disease in children.
In assessing whether women and girls were at higher risk for health burdens, most studies focused on children determining that boys were at greater risk for contracting both schistosomiasis (Kapito-Tembo et al., 2009;Ugbomoiko et al., 2009;Atalabi et al., 2016;Donohue et al., 2017) and hookworm infections (Baker et al., 2018) as well as stunting (Akombi et al., 2017) which is in line with a well-documented propensity for increased mortality among male children (World Health Organization, 2011). A single study directly analyzed the effect of gender on the frequency of waterborne diseases in adults, and found no gender differences (Al-Delaimy et al., 2014). However, numerous studies demonstrated that women's role as the primary water purveyor exposed them to multiple health risks. Women are at an increased risk of musculoskeletal disorders as a result of carrying water long-term and across long distances (Geere et al., 2018). Interestingly, males, but not females who fetched water >15 min, prioritized improving access to water over improving access to health services (Hunter, 2006). Women who fetched water from a drill pipe may also be at increased exposure to toxins, including lead as the blood of first-trimester pregnant women was recorded to have elevated levels of toxin lead (Guy et al., 2018). Also, how unclean water exposes households and adults more generally to toxins, such as Dichlorodiphenyldichloroethylene (DDE) and Dichloroduphenyltrichloroehtane (DDT) is documented by Gaspar et al. (2017). New mothers and pregnant women, in particular may represent a vulnerable population. For example, religious, new mothers who were fasting and did not have access to improved water or sanitation were more likely to be underweight (Desalegn et al., 2018). Furthermore, pregnant women who experienced a natural disaster reported a lack of access to basic water and maternal care which added physical and psychological stress (Sato et al., 2016).
A summary comparison of key gender, health and water differences from analyzed observational studies can be found in Table 3.

Both Infrastructural and Educational Interventions Are Successful in Reducing WASH Inequities and Improving Health Outcomes
To assess whether identified water-gender and health inequities can be addressed by currently administered interventions, we aimed to identify best practices themes from WASH interventions ( Table 2). Of the 13 interventional studies included, eight examined water access, eight assessed sanitation, six assessed hygiene, and one assessed MHM. Interventions were equally split between providing WASH education (N = 8) or providing physical infrastructural improvements (N = 9). The majority of studies (N = 9) considered how WASH interventions could improve health impacts.
Infrastructural interventions that improved water accessibility demonstrated mixed results for long-term benefits. Filtration systems provided to women were retained by 19 to 31% after a 2-5 years follow-up (Huq et al., 2010;Pickering et al., 2017). Similarly, the use of filters corresponded to small improvements in water quality (Huq et al., 2010), and a minor reduction in the incidence of cholera (Pickering et al., 2017). However, there remained a significant depreciation in the long-term usage of the interventions (Huq et al., 2010;Pickering et al., 2017). An intervention that provided mothers with treated water was successful in reducing diarrhea in school children by 40% and was considered a feasible solution by the participating mothers (Rose et al., 2006). Hand pumps were linked with overall healthier looking children (Katsivo et al., 1993). Furthermore, a comprehensive intervention which combined hand-pumps, latrines, and hygiene education demonstrated significant success after a 7-years follow-up, drastically increasing the number of households using improved WASH practices, reducing bacteria on the hands of mothers, and consequently the incidence of diarrhea in children (Hoque et al., 1996). 3 | A summary of key gender differences in access to WASH and health outcomes identified from assessed observational studies.
In addition to capacity, education represents a crucial component for improving WASH and has been incorporated as one branch of successful multifactorial interventions, for example, to overcome cultural apprehensions and misconceptions with using latrines (Yeasmin et al., 2017). Qualitative assessments of educational interventions suggest that education can reduce the incidence of diarrhea (Williams et al., 2015) and improve overall health (Magnin et al., 2018). Evidence that women were better than men at learning sustainable WASH practices through educational interventions has also been reported (Cairncross et al., 2005;Williams et al., 2015).

Assessment of Risk of Bias
In general, the included studies showed evidence for lower levels of bias. Across the 52 assessed cross-sectional studies, 41 (79%) were definitely or probably representative of the target population (Supplemental Table 1). The largest issues surrounded the reporting of participant non-response rates which was not reported by 15 studies (29%). To our assessment, all of the six included cohort studies likewise exhibited lower levels of bias (Supplemental Table 2). Finally, one study deployed a randomized control trial to assess the effectiveness of a school intervention, which, with the exception of evidence of blinding, exhibited lower levels of bias (Supplemental Table 3).

Summary of the Main Findings
This systematic review assessed WASH-related challenges faced by women and girls and further established a clear link whereby gendered WASH inequities interconnect with health outcomes, thereby establishing the "water-gender-health" nexus. We found some indication that women may have less access to clean water (Bisung and Elliott, 2018); however, few studies have directly interrogated this question. Regardless, women and girls typically served as the main water purveyors, a role which increased their risk for musculoskeletal trauma (Geere et al., 2018), and exposure to waterborne toxins (Gaspar et al., 2017;Guy et al., 2018). Additionally, a lack of latrines that are safe, secure, and private represents a major engendered barrier. The absence of such facilities forces women and girls to avoid practicing sustainable sanitation, hygiene, and MHM due to a fear of violence, or as a result of stigmatization (Kwiringira et al., 2014;Khan et al., 2017;Budhathoki et al., 2018;Davis et al., 2018;Winter et al., 2019). Poor WASH, in general, was linked to a multitude of health burdens, and particularly childhood diseases, including schistosomiasis, under-5 mortality, and stunting (Ahmed et al., 2016;Atalabi et al., 2016;Acheampong et al., 2017Acheampong et al., , 2018Akombi et al., 2017;Donohue et al., 2017;Vos et al., 2017;Baker et al., 2018;Marinda et al., 2018). WASH infrastructural and educational interventions in general showed promise in reducing inequities in the water-gender and related health outcome; however, issues surrounding long-term adoption reduced efficacy (Huq et al., 2010;Pickering et al., 2017).

Improving WASH Is a Critical Agent for Women's Health and Empowerment
Without explicitly searching for health-related outcomes, our search uncovered a significant overlap between WASH inequities among women and health, thereby linking the water-gender nexus with health. In support of our analysis, global reports have recognized that women and girls experience occupational hazards for waterborne diseases as a result of exposure to contaminated water and soils (World Health Organization, 2011). Irrespective of gender, the SDG six synthesis report (2018) has recognized handwashing with soap and water as a top priority for reducing disease transmission; however, gender disparities largely have not been recognized (United Nations, 2018).
Health burdens can significantly reduce human agency, for example, by reducing income and employment (Alam and Mahal, 2014). Considering that in low-resource settings women have reduced agency to make healthcare decisions, the impacts of disease and disability are likely to be further magnified (Osamor and Grady, 2016). Thus, addressing inequities in the water-gender nexus will have wider-reaching network effects, including supporting women's health, and by extension their empowerment, as outlined in various SDG five targets, including 5.c (i.e., adopt and strengthen sound policies and enforceable legislation for the promotion of gender equality and the empowerment of all women and girls at all levels). In addition, our analysis highlights a clear linkage between gender equitable access to WASH, and SDG 3.2 which aims to, by 2030, in all countries, end preventable deaths of newborns and children under 5 years of age, reduce neonatal mortality to at least as low as 12 per 1,000 live births, and to reduce under-5 mortality to at least as low as 25 per 1,000 live births. Thus, an enhanced understanding of interlinkages between water, gender, and health are increasingly relevant to, through a coordinated and integrated effort, achieving the SDGs.

MHM Is a Gap in the Sustainable Development Goals
Surprisingly, our analysis identified only a limited number of studies which addressed MHM. However, given that sustainability, and linkages with the SDGs was an explicit search term, the limited number of identified papers which assessed MHM practices perhaps reflects a more significant issue that MHM is not included clearly as an indicator within the SDGs portfolio (Anjum et al., 2019). The 2018 SDG 6 Synthesis Report more broadly describes how having access to safe drinking water and WASH in schools can improve school attendance by allowing girls to meet their MHM needs (United Nations, 2018). Likewise, other systematic reviews have concretely shown the implications of MHM on promoting education and good health among adolescent girls (Sommer et al., 2016). This principle can be expanded beyond schooling and into the workplace. In Bangladesh, where four out of five factory workers are women, more than two thirds loose 6 days of work in a month because of a lack of safe places to change their menstrual pads/cloths and the absence of disposal sites. Therefore, it is quite evident that addressing MHM needs is connected with women's access/capacity to gain education, employment, and financial capacity.
Recognizing this need, in 2012, Kenya launched the Sanitary Towel program to distribute sanitary towels to girls who attended school to support their education and to promote health and well-being. International Organizations have recognized the importance of MHM, including the United Nations Office for Coordination of Humanitarian Affairs (UN-OCHA), through forming humanitarian response plans, and these are part of a broader goal of addressing WASH needs.
Education and Long-Term Uptake Are Critical for Successful Interventions Our analysis of interventions to improve WASH can be successful in reducing both WASH inequities and disease; however, a focus is needed to ensure their long-term maintenance and usage. To this end, some reports indicated that women had greater levels of WASH knowledge and were better at retaining WASH-related education (Cairncross et al., 2005;Williams et al., 2015). This presents empowering women with WASH-related education as a simple, and feasible component for implementing successful interventions in the context of health and sanitationrelated challenges. This strategy has been embodied within SDG 6.b which calls for supporting and strengthening the participation of local communities in improving water and sanitation management. Our analysis supports global calls for gender mainstreaming and addressing gender inequalities in the water and WASH sectors.

A Dearth of Sex-Disaggregated and Unbiased Assessments of Sustainable WASH Accessibility
In clarifying the reliability of our identified findings, a majority of studies exhibited a lower risk of bias, often deploying appropriate sampling strategies. However, only half of studies directly compared WASH outcomes between genders, and <10% reported at least some gender-disaggregated data. Consequently, while we report examples of gender and WASH deficiencies, it is difficult to understand how women's access to WASH services, and corresponding health effects, differ from similarly situated men.
Recognizing this problem, in 2014, the UNESCO World Water Assessment Programme (WWAP) spearheaded the formation of the "Gender and Water Toolkit" which focused on understanding and furthering the gender-water-related research and investigation through the development of new sexdisaggregated indicators to more granularly enumerate genderdisparities related to WASH. As stated by the UNESCO/WWAP, "it is not an exaggeration to say there is virtually no sexdisaggregated data on water and sanitation sectors collected by the main international agencies and groups responsible for global data compilation." The 2nd edition launched in 2019 incorporates 105 indicators in 10 different topics related to the SDGs which includes water governance, safe drinking water, sanitation and hygiene, knowledge resources, transboundary water management, water for agricultural uses, water for industry and enterprise, and human rights-based water resource management. Future investigations which explore the watergender nexus should consider gender differences and sexdisaggregated data in their WASH analyses to better identify women specific barriers, as well as to elevate problems common to all gender groups.

Water, Gender, and Health Interconnect More Broadly With Other Goals Toward Sustainable Development
The SDG 6 synthesis reports that modest progress has been made to meet the targets of the 2030 Agenda; however, a specific focus on gender issues is lacking. All 17 SDGs are explicitly and implicitly related to water, while only a fifth of SDG indicators refer to gender or sex. Nevertheless, some of the major themes encapsulated in this review directly relate to established SDGs. For example, target 6.2 that highlights the importance of hygiene and calls for special attention to the needs of women and girls. Likewise, target 3.9 calls for substantial reduction of the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination, hazards which we contend represent occupational hazards for women and girls. It is also important to recognize that the interconnections that occur among SDG three, five, and six also extend to other SDGs, including; labor markets (SDG 8), political participation (SDG 10), poverty (SDG 1), peaceful and inclusive societies (SDG 16), among others. Future work should continue to elucidate these interactions.

Moving Forward: Addressing Stigma and Promoting Gender Mainstreaming
Gender-inequity is in part facilitated by stigma, engendered cultural norms, and a societal power imbalance. Stigma actively prevents women and girls from developing healthy habits (e.g., using soap and water or from using latrines (O'Reilly and Louis, 2014;Yeasmin et al., 2017;Winter et al., 2019). However, more than restricting access to WASH, stigma becomes an entrenched psyche, which actively promotes mental and physical distress and its pernicious effects can be readily seen with regard to MHM (Sommer et al., 2015a). For instance, girls' emotions surrounding MHM can include sadness, stress/anxiety, physical discomfort, feeling dirty, and shame, and consequently, engendered needs are often silenced (McMahon et al., 2011;Naeem et al., 2015). The stigmatization of menstruation can even result in women and girls exchanging "their bodies" for money in order to access resources for menstrual pads (Mason et al., 2013). As a result, even when capacity is available, stigma can undermine development efforts, and must be actively addressed. While methods to address stigma remain in their infancy, especially in LMICs, interventions are needed to raise awareness on the importance of engendered WASH priorities, to ensure that the needs of women and girls are underscored.
Reducing gender inequities will also inevitably require women to have a more prominent platform to advocate for the remediation of nuanced gender-barriers (Morna, 2000). In this respect, like others [Kholif and Elfarouk, 2014;Leahy et al., 2017;Dery et al., 2019; World Water Assessment Programme (UNESCO WWAP), 2019], we advocate for gendermainstreaming efforts when addressing WASH inequities. From ours and other's work it is clear that women occupy important WASH roles within households, both with fetching, storing, and using water (e.g., cleaning, cooking, washing, etc.) (Morna, 2000). Therefore, women and girls possess a particularly germane perspective which is needed to ensure that engendered WASHrelated barriers are elevated and considered by policymakers and decisionmakers. Including female perspectives may help elevate gender-based priorities (Dery et al., 2019), such as that when latrines are constructed, they include locks, are private, and are well-lit, in order to promote safety and therein increase access for women and girls. Thus, ensuring that a gendered perspective is included when developing capacity is essential to reducing engendered WASH inequities at scale.
Simultaneously, elevating women to leadership positions may aid in reducing cultural engendered power imbalances which actively suppress the human development of women and girls. Women and girls remain particularly disenfranchised, for example, due to their role as water purveyors and homemakers, gender roles which exacerbate the risk for health burdens (Sommer et al., 2015b;Gaspar et al., 2017;Geere et al., 2018;Guy et al., 2018), and sexual assault. Improving the status of women through gender mainstreaming represents an important first step in reducing the impact of cultural norms (UN Women, 2017). However, invariably, broader active efforts are needed to alter social behavior. While we recognize that behavioral change is a gradual process, sustainability and the empowerment of women will necessarily require efforts to break engendered cultural norms, and support the empowerment of women-critical steps to promote women's human development, and more broadly, sustainable development (Dery et al., 2019).

Strengths and Limitations of the Systematic Review
This analysis broadly combined qualitative investigation on the nuanced experiences of women with quantitative assessments on accessing sustainable WASH. While this afforded us a broad perspective on the array of WASH inequities faced by women and girls, we cannot effectively describe the magnitude of WASH deficiencies. As well, we did not exclude studies with high bias, and this limits the generalizability of our findings. We did not explicitly include keywords for health in our search strategy, which serves as a kind of prevalence calculation in order to supports broad interlinkages within the literature between gender, water, and health may limit the number of healthrelated studies identified. However, the use of the MEDLINE database likely adds a bias toward journal articles which consider health outcomes. As such, our findings should be viewed as a basis to enhance the understanding of the water-gender nexus, particularly within the sphere of related health outcomes. Finally, the search method was restricted to English, and thus, this is acknowledged as a limitation.

CONCLUSIONS
Major manifestations of the water-gender nexus include that women are burdened as a result of their role as water purveyors, a lack of private and secure latrines disproportionately impact women, and that women have less access to sustainable hygiene resources. In particular, there is a strong need for increasing MHM resources which are instrumental in supporting women's health, education, and human development. In general, we found a strong intersection between the water-gender nexus and health outcomes-the water-gender-health nexus. These include occupational health risks as a result of chronically carrying water and being exposed to contaminated water, as well as risks for infection due to poor sanitation and hygiene. Moreover, poor WASH practices among mothers are strongly linked with childhood diseases. Interventions were generally effective in reducing WASH inequities and poor health outcomes. To better understand the watergender and health interlinkages, there is a clear need for increased efforts toward sex-disaggregated data collection, as well as incorporating direct gender comparisons with respect to accessing and monitoring WASH services, and their associated health outcomes. This analysis supports the conjecture that addressing the water-gender nexus will help manage disease burdens and have a more significant impact on achieving the targets of SDGs three, five, and six in tandem.

DATA AVAILABILITY STATEMENT
The datasets generated for this study are available on request to the corresponding author.