Analysis of rainwater harvesting system in Katsina state, Nigeria

Abstract

Water is an essential resource for all life on the planet. Of the water resources on earth only three percent of it is fresh and two thirds of the freshwater is locked up in ice caps and glaciers. Of the remaining one percent, a fifth is in remote, inaccessible areas and much seasonal rainfall in monsoonal deluges and floods cannot easily be used. At present only about 0.08 percent of all the world’s fresh water is exploited by mankind in ever increasing demand for sanitation, drinking, manufacturing, leisure and agriculture. The available freshwater exploited is under stress due to increase in population and climate change. Water supply systems in many cities of the world are under stress. To tackle this problem, water authorities are adopting several measures including demand management and identifying alternative water sources such as rainwater harvesting. Rainwater Harvesting System (RHS) could be the best among the various technologies to augment freshwater resources in order to reduce the scarcity of safe water. Rainwater and its utilization could be an environmentally sound solution, which can avoid many environmental problems often caused by conventional large-scale projects using centralized approaches. The importance of roof rainwater harvesting as strategy to meet domestic water demand and to reduce run-off in built-up areas is growing worldwide. Indicators that measure the performance of rainwater harvesting systems have been developed. One such indicator is reliability, which is dependent on the rainfall and water consumption patterns, tank size and effective roof area. The application of an appropriate rainwater harvesting technology can make possible the utilization of rainwater as a valuable and, in many cases, necessary water resource. Rainwater harvesting has been practiced since antiquity, and in most developing countries, is becoming essential owing to the temporal and spatial variability of rainfall. Rainwater harvesting is necessary in areas having significant rainfall but lacking any kind of conventional, centralized government supply system, and also in areas where good quality fresh surface water or groundwater is lacking. Rainwater Harvesting System (RWHS) is basically a simple, technically feasible and socially acceptable system to store and use rainwater for drinking purpose Excel model that accounts for tank inflow and outflow and computes system reliability based on monthly rainfall data, effective roof area, monthly water consumption and tank size was developed. The model uses monthly rainfall data and parameters to calculate the reliability and x demand satisfaction of a given rainwater harvesting system, and output includes a graph of the system’s storage tank level over the simulation time period. Water demand is proportional to the storage capacity and hence the catchment area, the storage volume (liter) was determined for varying demand (liter per capita per day) for 5 number household and available roof area (m2) of 10, 15, 20, 30, 40 and 50 respectively. Storage may be tank or cistern, because the available polyethylene tanks in the market are 500, 1000, 1500, 2000, 3000, 4000 and 5000 liters which are the most common and easiest to clean and connect to the piping system. The rooftop area was multiplied by the annual rainfall and runoff coefficient to obtain the amount of water store Based on the results, a nomograph for reliability of 66.67% was developed. The nomograph was used to optimally size rainwater harvesting systems where the storage found to be 1000L. The higher the reliability, the greater the investment costs in water storage and roof area. , it is observed that the maximum reliability of the system is only 66.67%. Therefore, the water from supply main has to be used to fulfill the demand. The reliability can be increased by increasing the roof area and storage. Depending on the needs of your household, that can be significant amount of water to augment your water supply.