Other than modest amounts of local rainfall, all other surface water in northern Botswana comes from river catchments in Angola, and to a lesser degree from north-western Zambia. The four major river systems that supply water to Botswana are the Cubango and Cuito (which jointly supply the Okavango Delta), the Cuando (which provides the water of the Linyanti Swamps and Savuti Channel) and the Zambezi (which fills the Chobe river). The catchments lie either on shallow soils (much of the Cubango catchment and the eastern upper catchment of the Zambezi), or on deep sands (all of the Cuito and Cuando, part of the Cubango, and much of the Western Zambezi catchment). River discharges following rain from the former are relatively rapid, reaching northern Botswana towards the end of the rains. Those from catchments of deep sand are extremely slow, arriving in Botswana later during the dry months. Keywords: Okavango, Cubango, Cuito, Cuando, Zambezi.