Water availability in the root zone (‘green water’) is a critical component of plant production, but is often deficient in many Third World regions. When deficient, runoff water (‘blue water’) can be added. Focusing on ten physiographic regions in Africa and Asia, characterized by mainly or partly dry climates and rapid population growth, this study analyses whether in a 30–years' perspective enough blue water could be provided to allow food self–sufficiency. It is assumed that for food self–sufficiency some 900 cubic metres of water per person per year has to be provided. In judging the realism it is assumed that a maximum 25 per cent increase in water mobilization rate would be manageable in a 30–year period. The study suggests that by 2025, water scarcity will make regions populated by some 55 % of the world's population dependent on food imports. For water–wasting regions in Central Asia, water saving might, however, free the water needed. The paper closes by proposing some urgent measures.