Evaluating performance of rainwater harvesting technologies in Mwingi central sub-county, Kenya.

Abstract

The purpose of the study was to evaluate the performance of the rainwater harvesting (RWH) systems in the study area. An inventory of existing rainwater harvesting technologies and mapping of key watering points in the study area was conducted through a review of the literature, field observations, and interviews with key informers and administration of a household field questionnaire. The performance of the rooftop RWH systems was evaluated by establishing their technical feasibility, water saving efficiency, reliability ratio, and storage capacity ratio, while the modern demonstration farm ponds were evaluated on reliability only. Economic analysis of both rooftop and pond RWH systems at household level was done to determine their long-term viability through cost-benefit analysis. The research findings were that; Roof catchment systems were the most popular representing about 49% of the rainwater harvesting systems prevalent in the study area. The calculated mean annual household rainwater storage levels was 17. 72m3. The mean Annual roof runoff in the study area is approximately 76m3. The mean household water demand in the study area is approximately 40m3. This is approximately three times more than the current mean household water storage levels. The mean rooftop systems water saving efficiency was 44.85%, and mean reliability ratio of 24.72 categorized under very large deficit, meaning required water is largely higher than supply. The mean storage capacity ratio was 31.89, classified as very critical requirement, that is, the storage capacities are too small relative to the existing potential, this translated to 76.70% of the household rooftop RWHS being classified as of very critical requirement. The modern demonstration farm ponds had a reliability ratio of 1.0125, and were classified as highly sufficient. It was further established that both Rooftop and modern farm ponds RWHS were economically viable with high returns to investments. The research outcomes are a vital source of extra information for policy makers and engineers during the design and execution of RWH technology plans.