(introduction...)

Water conservation technologies cover all methods of conserving water through increasing water use efficiency, enhancing capacity to retain runoff water, and eliminating water pollution. Water use efficiency largely depends on availability and adoption of water saving devices and willingness of the consumers to reduce their total water consumption volumes. Furthermore, existing rules and regulations such as pricing mechanisms, reduce the total volume used, while economic incentives largely affect the choice and adoption of technology for water conservation technologies.

Water conservation processes can broadly be categorized into pre consumer and post consumer based approaches. Pre consumer based approaches involve increasing the efficiency of water extraction, storage and conveyance. Usually a large amount of water is lost either through evapotranspiration or seepage during transfer from the abstraction point to the point of use. It is estimated that, of the total rainfall in Thailand, about 70% returns to the atmosphere through the process of evaporation and transpiration (AIT, 1982). Using technologies that can minimize losses such as reducing evaporative losses from reservoirs, seepage losses from canals and water application losses prior to the water being used for economic purposes, can conserve a vast amount of water. In contrast, post consumer based approaches include the use of marginal quality waters, such as slightly saline water from the sea, untreated groundwater from shallow tubewells and rainwater collected from thatched roofs, for washing, toilet flushing purposes, etc.

In Asia, the agricultural sector consumes more than 75% of the total water withdrawn from all sources. About 60% of this water is lost during conveyance and distribution. Engineering technologies to reduce these losses, and to enhance utilization of water in irrigation schemes, are well studied and established practices which are beyond the scope of this book. In contrast, agronomic technologies such as efficient and modem methods of irrigation (including drip irrigation, sprinkler irrigation and surge irrigation) are less well-known and may be considered water conservation technologies. These technologies are documented in standard textbooks on agricultural and water resources engineering, and are briefly reviewed herein.

Recycling is also an alternative, post consumer technology for conserving and augmenting water supplies. It involves the reuse of water previously used for one purpose for a particular use in another application, before it reaches a natural waterway or aquifer. By using water several times, farms, urban areas and industries can increase the productivity of each litre of water consumed. Industries can conserve water by changing production processes from open to closed systems. In many industrial plants it is possible to recycle the cooling water. Some industries process water several times, and treat it at the end of its period of usefulness, prior to discharging the water to a natural water course. Reuse conserves raw water and, at the same time, reduces the volume of wastewater as well as wastewater treatment costs substantially. Several case studies on water conservation practices in India are described in Part C of this Source Book. In terms of particular technologies, there are no specific technologies involved, but rather a way of managing conservation practices in individual households and industries. Some of the technologies typically being practised in the Asian Region also are presented herein.