Water demands are outstripping supplies in many parts of Asia and causing conflicts, especially as rapidly urbanizing and industrializing areas compete with more traditional agriculture on alluvial plains near expanding metropolises. The environment is increasingly being seen as a legitimate and important user of water, often in competition with irrigation, domestic, industrial, hydropower and community uses of water. Any future scenario requires an improvement in water productivity, especially in agriculture. Surface and ground water supplies are not well regulated owing primarily to a weak knowledge base, analytical capacity in addition to a number of traditional institutional, governance, political and other factors. Water policy makers have, therefore, to work out strategies for integrated water and environmental management, which rely on a proper knowledge base of the basin hydrological and pollution conditions. Examples from various countries in Asia are elaborated in this paper to demonstrate how spatially distributed evapotranspiration data from remote sensing, in conjunction with other key data, can help to build the knowledge base for integrated basin scale water management. Remote sensing is not a solution, but it provides key data that is difficult to access by conventional data collection methods.