How did microbial contamination of urban water supplies change in Madagascar?

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In low-income countries, access to piped water is often limited to urban areas, and drinking-water microbiological quality varies because of technical and environmental constraints. To examine factors affecting contamination, researchers analysed 16 years of microbial quality data for water supplied in 32 urban areas of Madagascar. They applied a discriminant statistical approach and agglomerative hierarchical clustering to environmental and climatic data.

Microbial contamination varied between sites from 3.3% to 17.5%, and 78% of supply systems showed large variations between years or months. Agglomerative hierarchical clusters revealed four supply-system profiles with similar bacteriological evolution. Heavy rainfall and dry periods sustained increasing contamination, reflected in levels of spores of sulphite-reducing clostridia (SSRC) and/or total coliforms (TC). SSRC dominated in three profiles, while faecal indicator bacteria (FIB) dominated in the other.

Principal component analysis identified the main drivers of contamination as water source type, treatment implemented, site location, population growth, lack of protection, agriculture, urbanization/sanitation and flooding threats. Contamination increased over the 16-year period, reaching alarming levels. The authors concluded that water-source protection should be a concern for public authorities.