UC Berkeley

Access to safe drinking water remains a key concern across the globe. From the water source to the tap, many factors can influence microbial communities in water. This dissertation explores bacterial communities at various stages in the drinking water system serving the peri-urban region of Arraiján, Panama. First, the influence of land use and reforestation efforts on stream water bacterial communities was evaluated. Bacterial communities in the water column of four streams in the Panama Canal Watershed were assessed, each influenced by a different land use common in the Neotropics: mature forest, secondary forest, silvopasture and traditional cattle pasture. Land use was a key factor in microbial diversity and community composition. Streams influenced by forested areas exhibited diversity and community structure significantly different than streams influenced by lands with cattle. Reforested areas and agroforestry efforts such as silvopastures have the potential to protect water quality and significantly influence nearby water microbiomes.

Moving downstream in the drinking water system, the effects of water treatment and distribution were evaluated in the region of Arraiján, Panama, as well as the effects of intermittent water supply in a section of Arraiján’s drinking water distribution system. Treatment processes were determined to have varied effects on bacterial diversity and structure at the three different drinking water treatment plants surveyed. Water quality parameters such as chlorine concentration and temperature correlated with bacterial composition in treated drinking water. In the distribution system, bacterial diversity and structure varied spatially. Intermittent water supply significantly influenced microbial communities in drinking water, driving the proliferation of Pseudomonas and exhibiting higher number of unique bacteria that could result from intrusion or regrowth between supply cycles. Two key features of intermittent water supply were assessed in controlled laboratory bench-scale experiments: stagnation and drainage. Stagnation led to higher bacterial concentrations and significantly influenced bacterial diversity and structure. The effect of drainage was evident only in biofilm bacterial communities. The application of DNA sequencing to study source water and treated drinking water demonstrated the ability to characterize changes to the microbiome that would not have been evident through the use of traditional water quality parameters. This work provides helpful insights into drinking water bacterial communities in a tropical setting that could be useful for better managing water systems in similar settings.