Using solar disinfected water: On the bacterial regrowth over 1-week of water usage including direct intake after sun exposure and long-term dark storage

Abstract Safety and durability of solar disinfected water was studied along 1-week of simulated real water-usage. Water temperature during storage, microbial content and water quality were monitored. Initial raw water containing Escherichia coli and total coliforms were exposed to sunlight following SODIS guidelines and then stored prior to use. Simulated actions related to water usage were: direct human intake after disinfection (inoculating water sample in an enriched medium + incubation at 37 °C for 24 h); use of water from partially filled bottles that are back to storage again (water analysis from the same bottle over a week); and use of the entire water volume from fully filled bottles (water analysis from independent bottles over a week). Results show that SODIS treated water that achieved complete disinfection (0 CFU/100 ml) does not pose a health risk if consumed just after disinfection or stored in bottles carefully handled (either using partially or fully filled bottles) to avoid external contamination. For water that presents residual bacteria population after SODIS, regrowth might occur depending on water storage temperature, water nutrients content, storage period, and cells condition after sun exposure.