On-site sanitation and urban aquifer systems in Uganda

As part of a larger project aimed at designing a water source monitoring scheme for Uganda, data on bacteriological and chemical quality from protected springs and boreholes serving 4 towns were collected, and are here used as guides to what actions can be taken by town planners to minimize any health dangers there may be. The spring sources serving Kampala were analysed in the wet season, when rising water tables and agricultural runoff were most likely to produce flooding of latrines and the spring headworks. Only 2 per cent were free of contamination, 65 per cent showing coliform counts in excess of Ugandan guideline values, but a strong correlation was found between the contaminated sources and faults in their construction that had already been reported. In the other towns, where handpumped water was prevalent, borehole water was much better; again, faulty headworks correlated with contamination, the proximity of latrines seeming to have no effect (though data were collected in the dry season). Geological factors had a dominant influence on flow paths, and hence on the survival rates expected for bacteria from input site to abstraction point; standard bacterial indicators of pollution would not detect the presence of pathogenic viruses, and hence could not guarantee the safety of a drinking water source without treatment. Studies on correlation between contamination by nitrate and bacteria with population density in 2 areas of Kampala were being conducted, to assess the potential role of town planning regarding health in future urban growth, but it appears probable that, in already illegally inhabited areas, the concentration of human-derived nitrate in groundwater will necessitate water treatment as long as nitrate in drinking water is perceived as a health hazard.