Farmers could also reduce water withdrawal by scheduling their irrigation according to the actual weather conditions, evapo-transpiration rates, soil moisture and water requirement for particular crops. Co-ordination of the use and management of ground water and surface water can significantly increase the total efficiency of irrigation water in particular agricultural regions. Other available options to reduce the pressure of the demand for fresh water are the use of brackish water and the use of treated waste water for irrigation of salt-tolerant crops and for supplying certain industrial users. Brackish water for irrigation already plays a certain role in some countries, particularly in western Asia.
Recently, the cost/benefit issue has led to analysing irrigation investments in terms of grain prices needed to cover costs. In developing countries, capital costs for large-scale irrigation projects typically amount to some US$5,000/hectare, whereas those for small-scale projects such as tubewells and line lift pumps amount to only $1,000/hectare. In view of the cost differential, large incremental grain yields would be required to justify large-scale systems. In the past, large projects have contributed only 1/3-1 ton/hectare in yield increase as against a requirement of 2.5-15 tonnes/hectare to justify costs. It is therefore preferable both from the ecological and economic points of view to concentrate more efforts on irrigation systems that involve low capital costs.