Spatial model of groundwater contamination risks from pit-latrines in a low-income country.

Pit-latrines are central to achieving UN Sustainable Development Goal 6 (SDG 6) of ensuring "clean water and sanitation for all". Unless safely managed, pit-latrines result in groundwater contamination, which increases morbidity and mortality. Despite this, there have been no long-term spatial projections of future pit-latrine contamination risks. National survey data of over 100,000 water-points and 260,000 pit-latrines in Malawi was used to generate a novel, high-resolution model of pit-latrines from 2020 to 2070 under five population scenarios. The results here are presented as a 'business as usual' scenario of population growth and pit-latrine usage, predicting a three-fold increase in the number of current water-points at risk of short-distance microbial pit-latrine contamination between 2020 and 2070, with a seven-fold increase in number at the highest risk of contamination. Current nitrogen loading into pit-latrines is comparable to national fertiliser application. The model predicts 8.2 mega-tonnes of faecal nitrogen will be disposed of into subsequently abandoned pit-latrines between 2020 and 2070. Change is necessary to prevent SDG6's push for sanitation undermining its goal of clean water.