Almost nine-tenths of the caretakers in the Bamako, Mali site of the GEMS case-control study, used a municipal piped, treated water supply for their primary drinking water source. By WHO and UNICEF standards, this is an improved water source.2
Our study also found it was a safe source, with samples from all 63 randomly selected taps meeting the minimum recommended guidelines for free residual chlorine in piped, treated water (0.5 mg/L), and, with one exception, free from microbiologic contamination.28
Chlorine-resistant TCU were detected in water from one public tap, suggesting that biofilm contamination may be present in pipes supplying that tap. Biofilms are notorious in the water supply industry for growing on pipe surfaces and contributing to the survival and persistence of microbial contamination.30–32
Over a tenth of caretakers bought water from couriers who delivered water from this same municipal source. Because of the potential for introduction of contamination during collection and transport, water from couriers is considered by the WHO to be an unimproved water source. Water collected from couriers contained similar FRC levels as piped source water and 93% of samples were free from microbial contamination, suggesting that high FRC concentrations can help offset contamination risks posed by water vendors. The fact that one courier did introduce chlorine-resistant TCU contamination into the vended water supply is a reminder though that couriers could also introduce and transmit other chlorine-resistant fecal organisms such as Cryptosporidium. Overall, GEMS data suggest that piped water delivered directly from a tap or by courier to ~99% of the GEMS study population in two quartiers of urban Bamako meets criteria for safety and is an unlikely source of introduction of chlorine-sensitive diarrheal pathogens into households.
Although high quality piped water sources were generally pervasive throughout this community, a small subset of households did lack consistent access to their primary water source. Case-households had significantly less dependable access to their primary water source and had longer travel times to their water source than control-households. Longer travel times to a water source have been previously linked with increased diarrhea rates in children, and WHO and UNICEF define access to an improved water source as round-trip travel time of no more than 30 minutes from the household.2,33–35
Dependability and ease of access to a water source can impact water collection and storage practices. Dependable access to a nearby water source increases the volume of water available for household needs, and the frequency with which water is likely to be collected.34,36
Caretakers who had inconsistent access or had to walk > 30 minutes to fetch water were less likely to fetch water daily. Infrequent collection of water means that water must be stored in the home for longer periods of time, which in turn leads to lower FRC levels and increased risks of in-home contamination. Additionally, caretakers may be more likely to supplement water needs from poorer quality sources. Caretakers who use a piped source, who have daily access, or who require < 30 minutes to fetch water may also use a greater volume of water daily for washing and cleaning, which can also help reduce the risk of diarrheal diseases.37
Water collection and storage behaviors can also be influenced by motivations and perceptions caused by difficulties in accessing a safe water source.38
Caretakers with regular access to a nearby water source may still elect to spend less time, energy, or money going to the source to fetch and store water, resulting in less water used, longer water storage times, and possibly increased use of poorer quality secondary sources. All 48 caretakers in the nested sub-study reported having dependable access to their piped source, yet one-third still provided their child with drinking water that had been stored overnight or longer. In our multivariate model piped, treated water, dependable access to a water source within 30 minutes of the home, and fetching water daily, contributed independently to reduced risk of MSD in children. The nested study confirmed that fetching water less than once per day contributed to increased risk of fecal contamination in stored drinking water. Thus, access to an improved and safe water source alone, especially one that is not continuously available is insufficient to minimize diarrheal disease risk if safe behaviors for water collection, transport and storage are not practiced.
Data from the nested microbiologic sub-study shows how chemically and microbiologically improved source water can quickly deteriorate between point-of-collection and point-of-use, and how high FRC concentrations in piped treated water can partially mitigate that effect.39
Water storage in wide-mouthed containers that allow introduction of hands and objects, such as those used in virtually all GEMS Mali households, has been incriminated as a risk for microbial contamination of drinking water and for diarrheal disease.11,39–45,46,47
In our study, piped water that was stored in these containers showed a decrease in WHO recommended FRC concentrations and an 186-fold increase in microbial contamination in household water stored overnight. Despite this, water stored overnight in many households in unsafe storage containers still had > 0.2 mg/L of FRC (50%) and no detectable contamination (38%). Escherichia coli
was detected in stored water from only 4 (8%) of 48 households in the nested water quality study, all of which had stored water at least overnight and with FRC concentrations ≤ 0.2 mg/L. The low prevalence of fecal bacteria contamination is most likely caused by the lasting residual effects of originally high FRC concentrations in piped source water.28,29
The isolation of fecal E. coli
from stored water samples containing < 0.2 mg/L FRC reinforces current WHO standards for safe levels of disinfectant in stored drinking water.28
Improving access and availability of improved water sources, promoting more frequent water collection and the use of safe water storage containers by caretakers, and educating them about safe water handling could further reduce contamination of water in the home and the concomitant risk of waterborne disease transmission by pathogens, including those that are chlorine-resistant, within households.48–50
Modifying locally produced containers to include a smaller aperture and a spigot prevents the introduction of hands and objects into stored water, and may reduce the chlorine decay rate, thereby protecting the water from contamination during storage.51
Urban poor tend to pay more for water, in part because of a lack of access to private taps and subsequent dependency upon water vendors.52,53
The GEMS caretakers who bought water from vendors were more likely to belong to the poorest socioeconomic strata, even though water bought from a courier in Bamako costs twice as much as public tap water. These caretakers were particularly likely to fetch water less than once a day, suggesting that their water may be stored for even longer time periods than in households that collect water from a tap. Caretakers who pay more for water may be unable to afford to purchase water as often, leading to longer water storage times in the household and an increased risk of MSD among their children. For logistical reasons, we did not visit households using vended water during this sub-study. However, this population seems to be at increased risk for MSD and further studies should investigate the impact of economic and behavioral factors on water collection and storage practices in these households.52,53
Our findings have several limitations. First, water sampling was conducted during the dry season in Bamako. Piped distribution systems can experience a greater burden on chlorine demand during periods of high precipitation and ground saturation, so piped water quality in Bamako may worsen during the rainy season.9
Second, the nested environmental microbiology sub-study was conducted in GEMS households in two quartiers of Bamako after the child's enrollment in the case-control study, and therefore constitutes cross-sectional data in a portion of the city that cannot be causally linked to the original recorded health outcomes or generalized to the entire population of Bamako. Third, TCU and E. coli
indictor assays are useful for evaluating treatment efficacy for piped water and for tracking the microbiological deterioration of treated water in the home after procurement. However, the absence of coliforms is not a reliable indicator for the absence of contamination by chlorine-resistant microorganisms, such as Cryptosporidium
Fourth, the use of secondary sources for drinking water may be an important cause of exposure to waterborne pathogens. Although > 96% of caretakers reported having daily access to their primary water source, wells or other sources might be used if the primary source was non-functional, or if the caretaker lacked either the financial resources to pay for water or the time to fetch it. Caretakers may elect to save money and time by using secondary water sources for drinking, cooking, bathing, or hand washing. Data were not collected on the frequency with which water from secondary water sources was used for drinking. Nevertheless, this is an important issue that could influence the success of behavioral interventions. In addition, we did not collect data on the quantity of water collected or used per person in study households. Where water is scarce, hand washing and hygiene suffer and the risk of diarrheal disease transmission may increase.
Finally, even with broad access to treated source water, pediatric diarrheal morbidity and mortality in Bamako remain high. In addition to contamination of water during household storage, other routes of transmission of enteric pathogens (e.g., by contaminated food vehicles, fomites, flies, and direct fecal oral contact) are common in poor urban communities in the developing world, and are likely important contributors to the high rates of pediatric disease that persist in Bamako.54
Conversely, behaviors like breastfeeding can help protect infants and toddlers from disease through passive protection from antibodies and other factors in the mother's milk,55
and/or by reducing the likelihood that an infant will consume contaminated food or water. Our results concur with many other studies that children who are breastfed are protected against diarrhea, including when unsafe water practices are used. Environmental and behavioral interventions to diminish the pediatric diarrheal disease burden must be directed toward all of these modes of transmission.