Drivers of water quality variability in northern coastal Ecuador

Microbiological safety of water is commonly measured using indicator organisms, but the spatiotemporal variability of these indicators can make interpretation of data difficult. Here, we systematically explore the variability in Escherichia coil concentrations in surface source and household drinking water in a rural Ecuadorian village over one year. We observed more variability in water quality on an hourly basis (up to 2.4 log difference) than on a daily (2.2 log difference) or weekly basis (up to 1.8 log difference). E. coli counts were higher in the wet season than in the dry season for source (0.42 log difference, p < 0.0001) and household (0.11 log difference, p = 0.077) samples. In the wet season, a 1 cm increase in weekly rainfall was associated with a 3% decrease (p = 0.006) in E. coli counts in source samples and a 6% decrease (p = 0.012) in household samples. Each additional person in the river when source samples were collected was associated with a 4% increase (p = 0.026) in E. coil counts in the wet season. Factors affecting household water quality included rainfall, water source, and covering the container. The variability can be understood as a combination of environmental (e.g., seasonal and soil processes) and other drivers (e.g., human river use, water practices, and sanitation), each working at different time scales.