Report summary of WELL Task No. 163
Groundwater, latrines and health
Authors: Ben Cave and Peter Kolsky,
Editor: Darren Saywell
This study reviews the risks to health posed by groundwater contamination from on-site sanitation (particularly latrines) and attempts to consider it in the light of realistic alternatives. The study focuses on microbiological contamination because this is the most widespread and direct threat to health from on-site sanitation. The risks from nitrate contamination (the most frequent chemical contaminant of concern from pit latrines) are summarised in the report.
The key points to emerge from the discussion include:
- The key factor that affects the removal and elimination of bacteria and viruses from groundwater is the maximisation of the effluent residence time between the source of contamination and the point of water abstraction. Because of the very low velocities of unsaturated flow, the unsaturated zone is the most important defence against faecal pollution of aquifers.
- Commonly used guidelines in many soil conditions keep the bottom of the pit at least 2m above the water table, and at least 15m from any well used for drinking purposes. In some areas, such criteria cannot be met, or the soil conditions do not assure groundwater protection when the guidelines are followed. In these cases, the choice of sanitation technology depends on a variety of factors, including the relative risks of alternatives
- There are two main health risks associated with water quality degradation from on-site sanitation: faecal-oral disease transmission and nitrate poisoning. High nitrates can lead to methaemoglobinaemia, although this is a rare condition as compared with diarrhoeal disease.
- The common reaction that pit latrines are 'unacceptable' in dense urban areas because of the risks of groundwater contamination needs more critical examination. This response is often based on a number of unstated, untested and improbable assumptions about the causal chain of disease and the choice of sanitation technology.
- Planners should understand that any decision to ban on-site sanitation that leads, as a practical consequence, to a reduction in sanitation coverage is, in fact, a step backwards for public health.
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