Design of Rainwater Harvesting System: Basic Engineering and Economics

Residents at the Universal Primary Education (UPE) sand-filled of Borokiri town in Port Harcourt city, Nigeria are facing challenges in obtaining potable water due to numerous factors. Consequently, most residents could not meet the minimum daily per capita water demand set by the United Nations (50 – 100L). The rainfall in Port Harcourt is quite high enough to augment the water scarcity however, the poor quality of the rainwater makes it unsafe. Hence, rainwater harvesting (RWH) system incorporated with treatment facility was designed for an average household of six inhabitants at a daily per capita water demand of 75L. Results showed that the treated water obtained from the designed RWH system was highly potable and the reliability of the designed RWH system for water supply is 75% at a safety factor of 1.22. It was also found that the optimal dimensions of the rectangular rooftop gutters are 170mm width by 100mm depth (including freeboard space) at a bed slope of 1inch in every 10feet. The research further revealed that the designed RWH system is highly economically viable as the net present value (NPV), profitability index (PI) and payback period (PBP) are 747, 439.21Naira, 3.4 and 1.72years respectively, at a discount rate of 15% and lifespan of 15years. Necessary recommendations were made for the inhabitants of the study area, government and non-governmental organizations.