Methodological quality of the review: Medium confidence
Author: Stelmach RD, Clasen T
Geographical coverage: Not reported
Sub-sector: Trachoma, health effects and water quantity
Equity focus: None specified
Review type: Effectiveness review
Quantitative synthesis method: Narrative synthesis
Qualitative synthesis method: Not applicable
International efforts related to water in low-income countries often focus on the improvement of water supplies. While the quantity of water used in the home is thought to be an important determinant of health, much of the evidence relies on using water access as a proxy for quantity.
This review aimed to examine the health effects of household water quantity using studies that directly measured water quantity.
In total, 21 studies were included in the review. The studies took place in 14 countries, of which three are high-income, five are upper-middle or lower-middle income, and six are low-income. Fifteen of the 21 included studies were cross-sectional studies. The overall risk of bias for the included studies was generally high.
Overall, trachoma indicators were not found to be significantly associated with the amount of water brought to the house in most of the studies included in this review. Findings on the association between water usage and trachoma were mixed. In two studies which examined household water usage, authors noted that increased usage was found to be significantly associated with decreased incidence of gastro-intestinal (GI) illness.
Another study, which examined cooking and drinking water usage separately from bathing and washing water usage, found a significant relationship between shigellosis infection and water usage for bathing and washing, but only for those whose family contacts received a hand-washing training intervention. The amount of water consumed, however, was found in two studies not to have an association with incidence of diarrheal illness, and in one study, higher amounts of water consumed were actually associated with an increased incidence of acute GI illness.
Authors reported that findings of included studies also showed a positive association between higher water consumption and higher growth indicators. In addition, authors reported that higher levels of fluid consumption were found to be significantly associated with increased incidence of renal cell carcinoma and bladder cancer, but they were not found to be significantly associated with incidence of Type II diabetes.
Eligible study designs for inclusion included randomised controlled trials (RCTs); non-randomised studies with a control group including quasi-RCTs, non-randomised controlled trials, and controlled before-and-after studies; interrupted time-series; historically controlled studies; case-control studies; cohort studies; and cross-sectional studies. The exposure of interest was a measure change or difference in the quantity of water used in the home. The outcomes of interest were direct health outcomes measured at the individual or household level. There had to be at least one quantified measure of effect linking water quantity and the health outcome of interest.
Eligible languages for inclusion were English, French, Spanish, Portuguese and Italian. Only peer-reviewed, published records were considered. There were no restrictions on date or location.
The databases searched were the Cochrane Library—which includes the Cochrane Central Register of Controlled Trials (CENTRAL), the NHS Economic Evaluation Database, and the Cochrane Database of Systematic Reviews—EMBASE, MEDLINE via OVID, and Web of Science. In addition, authors reported reviewing one bibliography. Two authors independently screened studies for inclusion to assess the risk of bias of included studies using the WHO GRADE approach. Authors used a narrative synthesis approach to analyse the findings of included studies.
Authors stated that overall results showed a positive association between water quantity and health outcomes, but the effect depended on how the water was used. Increased water usage for personal hygiene was generally associated with improved trachoma outcomes, while increased water consumption was generally associated with reduced gastro-intestinal infection, diarrhoeal disease and improved growth outcomes.
Authors reported that for low- and middle-income countries’ communicable diseases examined (trachoma and GI-related illnesses), improved water quantity in the home often appeared to be significantly associated with improved disease outcomes. However, authors noted that in most cases this relationship depended on the manner in which water was used. For trachoma, authors noted that simply bringing more water to the house was not associated with improved trachoma indicators.
Authors stated that similarly, higher quantities of water in the home were generally associated with lower odds of diarrhoeal disease. In addition, they stated that the finding that increased water quantity was only associated with increased growth in families that owned a latrine reinforces the importance of integrating increases in the quantity of water available with improvements in sanitation and hygiene.
Summary of quality assessment:
Overall, there is medium confidence in the conclusions about the effects of this study. Authors did not conduct a thorough search of the literature to ensure that relevant studies were included in the review. Authors reported including peer-reviewed studies only, restricting the search to specific languages. Authors used appropriate methods to screen studies for inclusion and to assess the risk of bias of included studies.
However, it’s not clear from the review if two authors extracted data of included studies independently. Methods used to analyse findings of included studies were clear and authors made it clear which studies were prone to high or low risk of bias. Authors appropriately acknowledged the review’s limitations and did not draw strong policy conclusions.