Introduction

Cost–benefit analyses (CBAs) of water, sanitation, and hygiene (WASH) interventions have traditionally focused on two primary benefits: improved child health outcomes from reduced fecal exposure and reduced time burdens (Cha et al., 2020; Hutton, 2013; Hutton et al., 2007; Radin, Jeuland, et al., 2020; Radin, Wong, et al., 2020). Typically, child health benefits are measured by reduced cost-of-illness from diarrhea and mortality risk reduction, while reduced time burdens are measured by time savings from shorter water collection times and/or time to defecation site. While there is a large evidence base for both of these benefits, there is also growing evidence that improved WASH provides additional nutritional, educational/cognitive, and quality-of-life benefits, particularly for women. Considering these benefits in future WASH CBAs is critical to understanding the full scope of benefits that WASH interventions may offer. This article, first, briefly introduces the potential mechanisms for each of these benefits, before reviewing the current state of the literature and discussing how future WASH CBAs might incorporate each of these benefits.

The reduced fecal exposure from improved WASH decreases the risk of environmental enteropathy, a “syndrome of inflammation, reduced absorptive capacity, and reduced barrier function in the small intestine” (Crane et al., 2015, p. 1). Epidemiological evidence has shown that environmental enteropathy can result in stunting as well as increasing the odds of being underweight (Griffiths & Kikafunda, 2015; Guerrant et al., 2016; Lin et al., 2013; Mbuya & Humphrey, 2016; Petri et al., 2014). If WASH improvements can produce long-term benefits such as reduced stunting, then existing WASH CBAs may miss important long-term economic benefits associated with linear growth (Galasso & Wagstaff, 2019). However, there is mixed existing causal evidence on whether WASH interventions do, in fact, reduce rates of stunting (Cumming et al., 2019; Hammer & Spears, 2016).

Environmental enteropathy may also affect the cognitive development of children. Stunting resulting from environmental enteropathy is significantly associated with lower cognition (Berkman et al., 2002; Fischer Walker et al., 2012; Tartelton et al., 2006). Furthermore, cognitive development may also be affected by low-weight children suffering from nutrient absorption issues (Jiang et al., 2014; Petri et al., 2008). There is a growing causal empirical literature linking WASH, particularly improved sanitation, to long-term cognitive development (Orgill-Meyer & Pattanayak, 2020; Spears & Lamba, 2016). Additional research suggests that improvements in WASH, and sanitation in particular, improve school enrollment and attendance outcomes (Orgill- Meyer, 2020; Santiago Ortiz-Correa et al., 2016).

Finally, WASH improvements provide quality-of-life improvements, particularly for women. Improved sanitation, relative to open defecation, has privacy and dignity benefits that are acutely felt by women. Furthermore, beyond the commonly acknowledged time costs associated with gathering water or traveling to and from open defecation sites, women also face risks of assault and rape during these trips. Given the difficulty in quantifying such benefits, they have often been ignored or overlooked in CBAs of WASH interventions.

This article reviews the current state of the literature on WASH-related nutritional, educational/cognitive, and empowerment benefits. Additionally, it seeks to provide guidance on how to best incorporate these potential benefits into future WASH CBAs. It is important to note a few caveats. First, this article focuses exclusively on the benefits of household-level WASH. While there is a growing literature on the educational benefits of school sanitation (Adukia, 2017; Sclar et al., 2017), the focus here is on household and community-level WASH literature that can be extrapolated to future CBAs focusing on WASH interventions at the household or community level. Second, most of the literature measuring these three types of benefits—nutrition, cognition/education, and quality of life for women—focuses primarily on sanitation. While such returns might exist for water and hygiene interventions as well, these benefits are less studied in those contexts, and thus this article focuses more on the potential benefits of improved sanitation. Finally, there are growing empirical literatures for each of these potential benefits, and this article primarily restricts its review to peer-reviewed publications.

Nutrition and Stunting

Reduced diarrheal disease from improved WASH environments has implications for child nutrition. Epidemiological evidence suggests that children in environments with high levels of diarrheal disease are more likely to lose nutrients due to diarrhea; expend energy fighting diarrheal disease; contract worm and parasitic infections; and experience inflammation in the gut, causing malabsorption of nutrients due to repeated infections (Checkley et al., 2008). Indeed, chronic environmental enteropathy or environmental enteric infection from repeated exposure to fecal material has been shown to reduce nutrient absorption capacity and contribute to childhood stunting (Cumming & Cairncross, 2016; Humphrey, 2009). Linear growth and stunting are widely used biomarkers of environmental enteropathy (Keusch et al., 2013; Korpe & Petri, 2012; Prendergast & Kelly, 2012; Syed et al., 2016). Large-scale ecological analyses suggest a significant relationship between open defecation prevalence and childhood stunting (Spears et al., 2013). Furthermore, improved sanitation environments may result in reduced childhood anemia due to increased absorption capacity (Coffey et al., 2017).

Despite these potential epidemiological pathways through which improved WASH may improve nutritional outcomes, studies quantifying these benefits—child height and stunting in particular—have shown mixed results. A number of recent studies in India have shown a positive causal relationship between improved sanitation environments and child height (Augsburg & Rodríguez-Lesmes, 2018; Dickinson et al., 2015; Hammer & Spears 2016). Vyas et al. (2016) and Pickering et al. (2015) presented similar evidence from Cambodia and Mali, respectively.

Earlier randomized control trials showed no effect of sanitation interventions on child height outcomes (Clasen et al., 2014; Patil et al., 2014); however, uptake and compliance was low in both studies (Cumming & Cairncross, 2016). Three more recent cluster-randomized control trials with different WASH arms show no impacts of any of the WASH intervention arms on linear growth, despite high compliance with the interventions (Humphrey et al., 2019; Luby et al., 2018; Null et al., 2018). Only one of these trials also produced any significant changes in diarrheal disease outcomes (Luby et al., 2018), suggesting that the WASH interventions on their own may not have induced enough of a change in the disease environments to affect linear growth outcomes (Cumming et al., 2019). One potential reason for the lack of observed impacts on linear growth was low baseline rates of open defecation in two of the studies (Luby et al., 2018; Null et al., 2018) in comparison to studies that found a positive relationship between improved sanitation environments and child height outcomes (Coffey & Spears, 2018).

Looking beyond sanitation, there have been very few studies that explore the relationship between water and/or hygiene and child height outcomes. One randomized control trial of a solar disinfection intervention in Kenya found significant improvements to height-for-age Z-scores (Du Preez et al., 2011). Both Luby et al., 2018 and Null et al., 2018 found that the chlorine disinfection arms of their study had no significant impact on height-for-age Z-scores, though the combined water, sanitation, and hygiene arms did result in significant improvements. Other research investigating the role of water and/or hygiene on child height tends to be cross-sectional in nature (Rah et al., 2015; Torlesse et al., 2016), making it difficult to tease out the role of potential confounding factors.

Given the role that WASH, and sanitation in particular, may play in reducing malnutrition and stunting, how should analysts account for these benefits in cost-benefit analyses? Evidence suggests that even universal coverage of improved sanitation is insufficient on its own to eliminate childhood stunting (Bhutta et al., 2013). Table 1 summarizes the quasi-experimental and experimental studies discussed previously studying the effect of sanitation on child height to highlight the range of effect sizes observed in the literature. Taken together, the collective evidence suggests that a lower bound for the effect of improved sanitation on child height outcomes is zero. However, studies may have been limited in their ability to observe statistically significant effects due to low adherence and persistent open defecation (Patil et al., 2014) and/or low rates of baseline open defecation (Luby et al., 2018; Null et al., 2018). In the literature showing positive effect sizes, improvements to the sanitation environment (increases in sanitation coverage ranging from 10% to 100%) are shown to increase height-for-age Z-scores by 0.17 to 0.52 standard deviations.

The economic and monetary benefits of reduced childhood stunting are well-documented. Early-life stunting is strongly associated with poorer cognitive development (Kar et al., 2008) and lower educational attainment (Victora et al., 2008). Furthermore, growth failure early in life is strongly correlated with adult height (Alderman, 2010; Coly et al., 2006; Stein et al., 2010), and adult height is an important predictor of labor market outcomes (Deolalikar, 1988; Schultz, 2002; Thomas & Strauss, 1997). Because of these well-documented benefits, there is already a strong literature discussing the economic costs of early-life stunting and delayed growth (Alderman, 2010; Fink et al., 2016). Research from nutritional interventions found large long-term economic returns (Hoddinott et al., 2008; McGovern et al., 2017).

From one such nutritional intervention in Guatemala, researchers used instrumental variables to account for endogeneity of child height and found that a one-standard-deviation increase in height-for-age at 36 months of life increased hourly adult earnings by 14.8% and total per capita consumption by 19.5% (Hoddinott et al., 2011). They also found that per capita adult consumption was 66% lower among children who were stunted at 36 months of age compared to those who were not stunted (Hoddinott et al., 2011). Galasso and Wagstaff (2019) used a development accounting approach to compare countries with different levels of stunting and estimated a much lower benefit than what was found in the Hoddinott et al. (2008) and Hoddinott et al. (2011) studies. They found that adults who were stunted in childhood face an average income penalty of 5%–7% (Galasso & Wagstaff, 2019).

McGovern et al. (2017) provided a review of the literature on stunting and economic outcomes to consolidate estimates across several randomized control trials, quasi-experimental studies, and observational studies. They found that, on average, across these studies, a 1-cm increase in adult height is associated with a 4% increase in wages for men and a 6% increase in wages for women (McGovern et al., 2017). Combining these estimates with a study from Ghana showing that reduced childhood stunting is associated with a 6-cm gain in adult height (Schultz, 2003), Aryeetey et al. (2020) concluded that a reduction in childhood stunting results in an 30% increase in adult income.

Combining the range of potential effect sizes for child height returns from sanitation interventions with the economic literature on returns from reduced stunting introduced here provides researchers and policymakers with a way of incorporating nutritional and reduced stunting benefits into cost-benefit models of WASH interventions.

Cognitive and Educational Benefits

Quality of Life for Women

In addition to the nutrition, cognitive, and educational benefits that WASH may offer, there is also a growing literature documenting gender-specific benefits. Historically, this literature has focused primarily on the time-saving benefits of reduced water collection from improved water supply or reduced time to defecation sites from improved on-site sanitation options. More recently, research has found that open defecation causes a variety of psychosocial stressors for women. Indeed, women who rely on open defecation or shared community latrines report fear of being victim to crime or robberies (Khanna & Das, 2016; Shiras et al., 2018; Winter et al., 2018), physical violence (Abu et al., 2019; Kwiringira et al., 2014; Routray et al., 2015), and sexual assault (Hulland et al., 2015; Shiras et al., 2018). Additional research reports women feeling a loss of dignity and privacy from open defecation or shared latrine use (Azeez EP et al., 2019; Caruso et al., 2017; Schmitt et al., 2017).

There are some notable quantitative studies measuring the relationship between water access and quality of life measures for women. Choudhary et al. (2020) found that poor water access is positively associated with increased intimate partner violence in Nepal, perhaps due to women’s inability to complete certain household tasks such as cooking and cleaning that rely on water. This finding remains after controlling for a suite of covariates that might also affect intimate partner violence. Using a randomized control trial of access to credit for water connections in Morocco, Devoto et al. (2012) found that improved water access increases leisure time for women and reduces intra-household conflicts about water. Furthermore, women in households with higher levels of water insecurity are more likely to report being stressed and to score higher on depression scales (Aihara et al., 2016). Using an experience sampling method in Kenya, Cook et al. (2022) found that primary water collectors report lower levels of happiness, safety, and energy while participating in water-collecting activities. A randomized control trial of in-home water delivery confirmed these findings; individuals in households that were randomly assigned to receive water deliveries report higher levels of happiness, safety, and energy (Cook et al., 2021).

Reducing physical and sexual violence and providing improved safety, privacy, and dignity for women are obvious benefits that should be considered by policymakers considering WASH interventions. However, much of the research done in these areas to date is qualitative in nature, making it difficult to assess the extent to which switching to improved on-site sanitation options reduces the risk of physical and sexual violence. Where there is quantitative research, it is often cross-sectional and associational in nature, and the benefits are difficult to monetize. Thus, systematically including these benefits in a cost-benefit analysis is challenging. However, such benefits should not be ignored, and at the very least should be included as a benefit that is not quantifiable. For WASH interventions that do not appear to produce positive net benefits based on cost-benefit analyses, policymakers should consider whether such interventions are likely to provide some of the gender-specific benefits discussed in this section.

Conclusions

There is a growing body of research exploring WASH-related benefits that extend beyond the traditionally considered benefits of reduced diarrheal disease and time savings. Reduced fecal exposure from WASH interventions may decrease the risk of environmental enteropathy, resulting in nutritional status improvement. Causal research has provided mixed evidence for the direct link between improved sanitation, in particular, and stunting, though intervention adherence and baseline open defecation rates seem to play an important role in observing such a relationship. Beyond stunting, epidemiological evidence suggests that reduced environmental enteropathy can improve cognitive development, and indeed new research has established a direct causal relationship between sanitation environments and children’s subsequent cognitive development. Decreased illness incidence from reduced fecal exposure also seems to improve children’s educational outcomes, with improved household or community water and sanitation services being linked to increased school enrollment and decreased absenteeism. Finally, recent qualitative literature has shown that both sanitation and water security can have important quality-of-life benefits for women in particular. Women practicing open defecation or using shared latrines report concerns about theft, physical violence, and sexual assault. Women in households with high levels of water insecurity are more likely to face intimate partner violence and depression.

Incorporating the wide-ranging benefits of WASH interventions into systematic CBAs can be challenging. Much of the literature is still new, so analysts must rely on relatively few studies for ranges of plausible benefits. While existing economics literature has produced credible monetary estimates for the returns of increased stunting and increased educational attainment, there are fewer estimates that monetize the benefits of improved cognition and reduced concerns of physical or sexual assault. Based on the available literature, CBA practitioners should incorporate stunting and educational attainment benefits into sensitivity analyses of WASH CBAs. Additional research is needed to monetize the benefits of improved cognition and improved quality of life for women. However, it is important for analysts to flexibly consider these types of benefits as potentially non-monetizable benefits in WASH CBAs, that likely still enlarge the net present value of WASH interventions.

Further research both quantifying and monetizing these types of benefits is needed to add additional credibility to the range of potential benefits. Research on cognitive returns to WASH interventions and the monetary returns associated with particular cognitive measures is particularly needed. Additionally, while there has been excellent qualitative research exploring women’s safety and privacy concerns with open defecation and shared sanitation, quantitative research is needed to measure how much improved sanitation decreases risks of physical and sexual violence. Finally, in all of these domains—nutrition and stunting, cognition and education, and quality of life for women—the majority of research focuses on improved sanitation. Future research should explore the extent to which improved water supply, improved water quality, and hygiene interventions might also produce similar returns.