GROUNDWATER QUALITY IN NEPAL'S KATHMANDU VALLEY: AN ASSESSMENT OF CONTROLLING SITE CHARACTERISTICS

Nepal’s population has grown by 28% in the past decade and about 50% of the population of Nepal relies on groundwater for its drinking water supply. As Nepal’s population grows, the municipal systems cannot keep up with demand, so there is a continuing and even increased reliance on private wells and public dharas (stone spouts tapping groundwater). Many people face severe health threats stemming from water contaminated by sewage, agricultural practices, and industry. Over 26% of the total groundwater withdrawn from the Kathmandu Valley is from private wells, and over half of these are very shallow and prone to contamination.

In May-June 2001 we conducted a groundwater survey of over 100 water sources including public stone spouts, municipal taps, dug wells, and tube wells. At each water source we measured and obtained through interviews site characteristics including the type, age and depth of the well, depth to water table, age of settlement, drinking water preferences, perceptions of water quality and proximity to potential contamination sources. A water-quality field kit was used to measure the concentrations of nitrate, nitrite, ammonia, phosphate, sulfate, manganese, iron, fecal coliform, and E. coli, all indicators of contamination from sewage, agriculture, and/or industry. Samples were also brought back to the USA for heavy-metal analysis on an ICP-MS.

Preliminary results indicate every drinking-water source had total coliform contamination, but statistical analyses reveal significant differences in contamination levels between public stone spouts, municipal tap water, dug wells and the private tube wells; dug wells are the most contaminated. Interestingly, when people have a choice of different water sources, on average they choose the more contaminated source with respect to fecal coliform. This may be due to the fact that a taste-based preference is given to shallower water with lower iron content, but higher levels of fecal coliform. Statistical analyses show increasing Fe content with depth and an inverse relationship between Fe content and fecal coliform levels.

In private dug wells, nitrate and phosphate levels were both found to significantly decrease with distance from the nearest pit toilet or municipal sewage pipe. No such relationships, however, were found for bacteria.