Water is essential to sustain life, and adequate, safe and accessible supply must be available to all. Millions of people throughout the world do not have access to clean water for domestic purposes. In many parts of the world, conventional piped water is either not available, unreliable or too expensive. One of the biggest challenges of the twenty-first century is to overcome the growing water shortage. Rainwater harvesting (RWH) has thus regained its importance as a valuable alternative or supplementary water resource, along with more conventional water supply technologies. Much actual or potential water shortages can be relieved if rainwater harvesting is practiced more widely. Severe water shortages and extremely fragile ecological conditions necessitate careful attention to water resources conservation and management. Nowadays, cumulative effects of climate change, population increase, development, and industrialization are leading to increased water demand which seeks careful and strategic management of the available resource. In the Ethiopian context, the average annual population growth is about 2.8% and twice of water demand increase. People collect and store rainwater in buckets, tanks, ponds, and wells. This is commonly referred to as rainwater harvesting and has been practiced for centuries. Rainwater can be used for multiple purposes ranging from irrigating crops to washing, cooking and drinking. In this paper, assessment and review are done on effects of climate change, population growth and development on water demand increase. Long-term average annual rainfall was accessed from meteorological data, and minimum numbers of houses data were taken from Ethiopian 2007 census data. Finally, possible amount of water harvested is estimated for domestic and other water uses.
