This study was requested by HE Amani Adied Karume, President of Zanzibar. The terms of reference were prepared and commissioned by the MDG centre based in Nairobi in collaboration with UNDP Tanzania to explore the prospective of improving water availability and management in Zanzibar through application of rainwater harvesting and management technologies. Zanzibar is comprised of two island; Unguja of 1658 km2 and Pemba of 985 km2. The islands are located 40 kilometres off the mainland Tanzania coast, 5 degrees and 6 degrees south of the Equator. The 1999 census estimated the population of Zanzibar at 916,000. According to the Household Budget Survey report release in September 2006, 49% of the population lives below the basic needs poverty line. The report further found that the incidence of poverty was higher in rural compared to urban areas. Agriculture is the main occupational activity, employing more than a quarter of the total labour force in Zanzibar. In the year 2000, agriculture contributed 36% Gross Domestic Product (GDP) and about 90% of the total foreign exchange earnings. However, agriculture is propelled by poor smallholder farmers producing under rain fed conditions using traditional methods. According to Johnson 1994, both islands are fertile due to the rich soils derived from weathering of main sedimentary rock sequence. Zanzibar is also endowed with high mean annual rainfall of up to 1900mm.Water balance studies conducted by the Ministry of Agriculture, Natural resources, Environment and Cooperatives (MANREC) and JICA suggest that Zanzibar looses on average 50% of the total rainfall received through runoff via rivers to the sea. Only 24% in Unguja and 7% in Pemba ends up in groundwater. Given that Zanzibar’s main water sources is groundwater, there is great need to introduce rainwater harvesting technologies in order to improve water availability, especially for agriculture which takes up the largest proportion of the island’s water.