Angola is endowed with substantial surface water resources, with all the major rivers (apart from the Zaire and Chiluango of' Cabinda) originating within the country, The majority of rivers rise in the mountainous coastal ridge, with those flowing into the Atlantic being relatively short and those flowing east and north forming longer systems (Cuban go and Cuando). Groundwater is utilised for several urban centres on the coast and in the arid southern provinces and is a major source for rural supply. Additionally, small groundwater based systems have recently been developed to assist in the water supply shortfall in growing peri-urban areas. The overall potential of both surface and ground water is largely untapped, primarily due to long-term instability jn the country.