ABSTRACT
The Quantitative Microbial Risk Assessment (QMRA) technique is used to enhance water safety planning and evaluate microbial risks, in which anticipated health implications are explicitly quantified. Roof-harvested rainwater (RHRW) in the Ikorodu neighbourhood of Lagos State, Nigeria, is evaluated in this chapter, and recommendations to reduce adverse health risk to the residents are proposed. In the study region, various types, designs, and uses of rainwater harvesting systems have been assessed to determine the risk of human exposure to Escherichia coli (E. coli). To accomplish these objectives, a thorough survey of 125 households was conducted, and outcomes revealed that 25% of respondents consume RHRW. The risk of exposure to hazardous E. coli from RHRW utilised as potable water has been quantified using QMRA methodology, based on the use of 2 L of rainwater per day per capita. The highest E. coli exposure risk from consuming RHRW, both without the use of any household water treatment techniques (HHTTs) and with the use of alum treatment, was determined to be 100 and 96, respectively, for the projected number of infection risks per 10,000 exposed households per year. This estimated QMRA was obtained based on the premise that 7% of E. coli is viable and harmful. To reduce the risk of exposure to harmful E. coli, RHRW must be treated with an appropriate disinfectant prior to use.
