In order to ensure that the finite amount of water that is available in the hydrological cycle is adequate to meet the still growing demand for water, it is absolutely necessary to reverse past trends in water consumption, find innovative ways of conserving water and develop new water supplies. Both the development of water resources and the use of water – i.e. the supply side and the demand side of water – need to take into account likely adverse impacts on the environment generally and on land resources in particular. Economic activities and municipal use of water need to ensure that bodies of water are kept free of pollutants so that the stock of water is available for careful use.
This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends implementation of allocation decisions in water resource management through demand management, pricing mechanisms and regulatory measures.
The most immediate course of action must centre on water conservation, through rational utilization of water resources and technical innovations. In many industries much of the water used for cooling and other processes does not need to be of drinking quality. A large proportion of water initially withdrawn for industrial purposes can be recycled several times before it is finally disposed of. The efficiency of water technology can be increased further by such means as totally integrated water-recycling systems. While the scope for waste-water re-use so far is relatively small in developing countries, since many of them do not have sewerage systems that collect the used water, there is large scope for building new industries with water recycling systems. Moreover, domestic waste water could be collected and used after treatment for agricultural purposes.
The need for raising the efficiency of irrigation is even more compelling, since irrigation claims the bulk of most countries' water supplies and is generally rather inefficient. Saving even a small proportion of the water used in irrigation will free a large absolute amount of water for other needs. 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. Increasing the efficiency of irrigation would call for improvement in technical infrastructure and adoption of more efficient management methods. Even more effective would be avoiding the use of more water than is necessary, through the assessment of water needs for crops in various places, education of farmers on optimal use of water, and adoption of more efficient irrigation technology. 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.
The municipal use of water, including household use, is much less than agricultural or industrial. Storing, treating and distributing municipal water and collecting and treating the resulting waste water is, however, increasingly costly and may in some cases entail large capital investments. Conserving water and increasing the efficiency of municipal water use would ease the financial burdens by enabling water and waste-water utility companies to scale down the capacity for new plants, water mains and sewer pipes and also cut energy and other costs for purification technology associated with municipal water supplies. Efficiency of use can be increased by reducing losses in the distribution system and by improving household fixtures and appliances, especially flushing toilets, dishwashers and washing machines.