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10th International Rainwater Catchment Systems Conference
"Rainwater International 2001"
Mannheim, Germany - September 2001

Section 2: Rainwater Catchment in Humid and Arid Regions

Paper 2.20

Rainwater as a Supplementary Source of Water Supply in Nigeria

Joseph A. Adelegan
Department of Civil Engineering
University of Ibadan


Over the years, the Federal Government of Nigeria has made appreciable investments towards development and management of water supply using large centralised and conventional water supply systems. For certain reasons, the demand for safe drinking water service continues to overwhelm the delivery. Though for centuries, people across Nigerian urban and rural areas have harvested rainwater for household, livestock and agricultural uses but lack of promotion had limited its wide acceptance especially in urban centres. The study looks into rainwater availability, rainwater catchment, storage tank capacity and rainwater quality.

Major data used for the work include an average of 35 years rainfall pattern based on yearly rainfall intensity for 18 Nigerian cities and major towns obtained from Nigerian Meteorological Centre records. The variations and distribution of rainfall in the cities and towns studied were plotted. Permanent roofs for rainwater harvesting were also assessed. Moreover, the issue of rainwater quality was also considered.

It appears that the average yearly rainfall in Nigeria during the period examined varied from 1070mm to 2400mm, that is, 1.07 to 2.40m3 of rainwater was available per m2 of catchment area each year for the development of a rainwater based water supply system. A study of suitable permanent roofs for rainwater harvesting shows that over 75% of urban households and about 20% of rural households have suitable roofs.

A rainwater availability mass curve and cumulative consumption / demand of total rainwater revealed a shortfall of 0.32m3 in the dry periods and an excess of 0.22 m3 during rainy season. Hence, for full utilisation of rainwater potential, a storage tank capacity of 0.54 m3, that is 33% of the cumulative rainwater is required for an uninterrupted water supply at a constant rate during the year.

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