Microbial contamination of drinking water from risky tubewells situated in different hydrological regions of Bangladesh

This study, conducted in 40 selected upazilas covering four hydrological regions of Bangladesh, aimed at determining the risk of selected shallow tubewells (depth <30m) used for drinking purpose (n = 26,229). This was based on WHO's sanitary inspection guidelines and identifying the association of sanitary inspection indicators and risk scores with microbiological contamination of shallow tubewells. The main objective of the study was to observe the seasonal and regional differences of microbial contamination and finally reaching a conclusion about safe distance between tubewells and latrines by comparing the contamination of two tubewell categories (category-1: distance ≤10 m from nearest latrine; n = 80 and category 2: distances 11-20 m from nearest latrine; n = 80) in different geographical contexts. About 62% of sampled tubewells were at medium to high risk according to WHO's sanitary inspection guidelines, while the situation was worst in south-west region. Microbiological contamination was significantly higher in sampled category-1 tubewells compared to category-2 tubewells, while the number of contaminated tubewells and level of contamination was higher during wet season. About 21% (CI95 = 12%-30%), 54% (CI95 = 43%-65%) and 58% (CI95 = 46%-69%) of water samples collected from category-1 tubewells were contaminated by E. coli, FC, and TC respectively during the wet season. The number of category-1 tubewells having E.coli was highest in the north-west (n = 8) and north-central (n = 4) region during wet season and dry season respectively, while the level of E.coli contamination in tubewell water (number of CFU/100 ml of sample) was significantly higher in north-central region. However, the south-west region had the highest number of FC contaminated category-1 tubewells (n = 16 & n = 17; respectively during wet and dry season) and significantly a higher level of TC and FC in sampled Category-1 tubewells than north-west, north-central and south-east region, mainly during wet season. Multivariate regression analysis could identified some sanitary inspection indicators, such as tubewell within <10 m of latrine, platform absent/broken, pollution source (i.e. household's waste dumping point/poultry/dairy farm) within 10 m of tubewell and unimproved sanitation facility which were significantly associated with presence of microbial contaminants in tubewell water (p < 0.01). A tubewell with high risk level was associated with a higher chance of having FC and TC in tubewell water than a tubewell with a medium risk during wet season, but no such conclusion could be drawn in case of E.coli contamination. Construction of pit latrine in areas with high water table should be highly discouraged. Raised sealed pits or flush/pour flash to septic tank could be installed considering sanitary inspection criteria. Water should be treated before drinking.