This paper shows that water scarcity is a complex problem when it affects countries with a semi-arid climate, ie countries for which there are fluctuations between a dry season and a season when rain occurs. The paper discusses the general vulnerability of the semi-arid zone in terms of four different types of water scarcity, the effects of which are being superimposed on each other: two are natural (type A, arid climate, type B, intermittent drought years) and two are man-induced (type C, desiccation of the landscape driven by land degradation, and type D, population-driven water stress). When fuelled by a rapid population increase, a risk spiral develops, manifesting itself in social and economic collapse during intermittent drought years. The paper concludes that many countries in Africa are heading for severe water scarcity -in fact two-thirds of the African population will live in severely water-stressed countries within a few decades. This severe water stress will largely be the result of unfettered population growth.