Water scarcity is among the many problems faced today by many countries in the world, especially African countries. The Kakamega area in western Kenya is known for plenty of rainfall (around 2000 mm annually), however, rainwater harvesting (RHW) from roofs is not yet a common practice in the region. In this study, we determined the potential of RWH as an alternative or preferred source of safe water for domestic use. Spatial modelling techniques using amount of rainfall, census data and detailed information available from the classification of very high resolution QuickBird satellite imagery as input data were applied to implement various approaches. Four conceptual models were developed at three different levels of detail: the Kakamega-Nandi forests area (3900 km²), the QuickBird imagery covered area (473 km² of farmland) and Buyangu village (1.9 km²). The four models were implemented in ArcGIS ModelBuilder and reveal the potential of such spatially explicit simulations to guide planners and to demonstrate the benefits of RWH to the local people. In the Kakamega-Nandi forests area, it rains enough to meet the annual water demand of 7300 l per person almost throughout the entire area.