Ensuring access to safe drinking water is a key strategy for reducing waterborne illness. The WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation (JMP) differentiates between unimproved and improved sources to universally classify water access. This classification, however, is based on the type and location of the water source and does not take into account water quality; even sources classified as improved can have compromised water quality and pose a health risk from waterborne illness.
One type of improved water source in urban settings is piped drinking water on premises. However, the presence of a piped connection gives little information about the quality, quantity and frequency of water delivery. Even in settings with centralized water treatment, piped water distribution systems are vulnerable to performance deficiencies that can cause (re)contamination of treated water and plausibly lead to increased risk of gastrointestinal illness (GII) in consumers. It is well established that large system disruptions in piped water networks can cause GII outbreaks. We hypothesized that routine network problems can also contribute to background levels of waterborne illness and conducted a systematic review and meta-analysis to assess the impact of distribution system deficiencies on endemic GII. We reviewed published studies that compare direct tap water consumption to consumption of tap water re-treated at the point of use (POU) and studies of specific system deficiencies such as breach of physical or hydraulic pipe integrity and lack of disinfectant residual. In settings with network malfunction, consumers of tap versus POU-treated water had increased GII (IDR = 1.34, 1.00-1.79). The subset of non-blinded studies showed a marked association between GII and tap versus POU-treated water consumption (IDR = 1.52, 1.05-2.20); there was no association in studies that blinded participants to their POU water treatment status (IDR = 0.98, 0.90-1.08). Among studies focusing on specific network deficiencies, increased GII was associated with temporary water outages (RR = 3.26, 1.48-7.19) as well as chronic outages in intermittently operated distribution systems (OR = 1.61, 1.26-2.07). These findings suggest that tap water consumption is associated with GII in malfunctioning distribution networks. System deficiencies such as water outages increase the risk of GII, presenting a potential health risk for consumers served by piped water networks.
Additionally, intermittent delivery of piped water is a common form of water supply in low-income countries. Intermittent supply can lead to waterborne illness through contamination of water in pipelines or in household storage, use of unsafe water sources during intermittencies and limited water availability for hygiene. To assess the health impact of intermittent water delivery as a particular type of breach of hydraulic pipe integrity, we conducted a matched cohort study to assess the impact of switching from intermittent to continuous water supply in Hubli-Dharwad, India, on child diarrhea and mortality, and severe waterborne illness in tap water consumers. We used multivariate matching to match continuous supply areas to intermittent supply areas with comparable baseline characteristics in Hubli-Dharwad. We followed 3919 households with children under five over 15 months. In continuous supply areas, we observed 42% reduction in the percentage of households with at least one case of typhoid fever since the program was implemented (CIR = 0.58, 0.41-0.78) and potentially 49% reduction in the percentage of households with death of a child under the age of two (CIR = 0.51, 0.22-1.07). Consistently with these reductions, our findings also suggested reductions in seven-day prevalence of diarrhea (PR = 0.93, 0.83-1.04) blood or mucus in stool (PR = 0.78, 0.60-1.01) in children under five in continuous supply areas. These reductions were more pronounced in low-income households (diarrhea PR = 0.89, 0.76-1.04; blood/mucus PR = 0.63, 0.46-0.87). The effect of rainfall on the impact of continuous supply on child waterborne illness was inconclusive. Our findings indicate that switching from intermittent to continuous water supply reduced waterborne illness in Hubli-Dharwad.
Another type of improved water source, commonly used in rural settings, is tubewells that draw groundwater from shallow aquifers. Shallow tubewells are the primary drinking water source for the majority of rural Bangladeshis. While groundwater is often considered microbiologically safe, fecal contamination has been detected in tubewell water, typically at low concentrations at the source and at higher levels at the point of use. The magnitude of the waterborne disease burden associated with consumption of tubewell water is not well understood. We conducted a randomized controlled trial to assess whether improving the microbial quality of tubewell drinking water by household water treatment and safe storage would reduce diarrhea in children <2 y in rural Bangladesh. We randomly assigned 1800 households into one of three arms: chlorine plus safe storage, safe storage and control. We longitudinally followed households with monthly visits for one year to promote the products and collect health outcomes. Both interventions had high uptake in the study population. Safe storage, alone and in combination with chlorination, reduced heavy contamination of stored water. In the chlorine plus safe storage arm, 2% of stored water samples had E. coli concentrations exceeding 100 CFU/100 mL, compared to 7% in the safe storage arm and 21% in the control arm. Compared to controls, diarrhea prevalence in children <2 y was reduced by 36% in the chlorine plus safe storage arm (PR = 0.64, 0.55-0.73) and 31% in the safe storage arm (PR = 0.69, 0.60-0.80); there was no difference between the two intervention arms (PR = 0.92, 0.79-1.08). Our findings suggest that safe storage significantly improved drinking water quality and reduced child diarrhea in rural Bangladesh. There was no added benefit from combining safe storage with chlorination.
Taken together, this body of evidence confirms previous findings that, even for water sources categorized as improved by the JMP, there are water quality problems that can pose a public health threat. Our findings highlight deteriorations in water quality associated with deficiencies in the distribution and handling of drinking water from the point of source to the point of consumption, rather than contamination at the water source. These findings suggest that efforts to improve drinking water quality should place emphasis on preventing contamination at each step of the chain leading from the water source to the point of consumption, including the distribution system and household storage containers, to maximize the protection against waterborne illness.