Field assessment of solar disinfection of water in Obunga slum, Kisumu, Kenya: comparative insights from Nairobi pre-trial data

ABSTRACT Schematic illustration showing microbial contamination of shallow wells in Obunga slum and solar disinfection (SODIS) using PET bottles under sunlight, resulting in microbial inactivation. The diagram highlights differences in UV-A exposure between Obunga and Nairobi, indicating the need for site-specific treatment conditions. Globally, 2 billion people lack access to safe drinking water, particularly in Sub-Saharan Africa, where 50% of the population relies on unsafe sources. In Kenya, particularly, informal urban settlements are burdened by diarrheal disease, with very few Solar Disinfection (SODIS) water interventions. This study assessed the effectiveness of SODIS as a low-cost household water treatment method in Obunga slum, Kisumu. Water samples were collected from four commonly used ground sources and placed in two-litre polyethylene terephthalate bottles. These bottles were then exposed to direct sunlight for six hours. SODIS achieved a 4-log reduction value in E. coli (99.99%, p = 0.001) and a 0.81-log reduction value in total coliforms (84.64%, p = 0.001). Comparative pre-assessment in Nairobi under similar SODIS conditions showed that the lethal UV-A dose in Obunga slum was significantly higher, reflecting site-specific water quality factors that reduce UV penetration, highlighting the need for localized SODIS protocols. These findings highlight the potential of SODIS to improve microbial water quality in Kenyan informal settlements. Interventions for the scaling up of SODIS through community sensitization and integration into water safety policies should be prioritized to enhance uptake and sustainability, thereby reducing the burden of diarrheal disease in informal settlements.