- To supplement the water from rivers, lakes, reservoirs and aquifers, the demand for water could be met by water transfer, estuary storage, conjunctive use, desalination, rain-making and conservation.
- Water transfer takes water from an area of surplus to an area of deficit. It has the disadvantages that it is very expensive to transport water large distances and that it may cause environmental side-effects.
- Storing water in an estuary makes it possible to use water that would otherwise be lost to the sea. It avoids flooding large areas of land for reservoirs, and the water is available where there is a demand for it. The disadvantages are that water has to be pumped up to land, the quality will be poor, estuary navigation may be restricted and there may be ecological consequences.
- Conjunctive use is the combined use of surface water resources and groundwater to provide a better or more flexible water resource. Two types of conjunctive use are managed aquifer recharge and river augmentation. Managed aquifer recharge is the replenishment of an aquifer in excess of natural infiltration, by storing surface water underground when surface water is abundant. River augmentation is used to increase the flow of a river at times of low discharge. The aquifer and river can each be used directly, but at different times of year.
- Desalination makes seawater usable for water supplies. The process consumes a lot of energy, so it is one of the most expensive ways of producing fresh water.
- Rain-making is an artificially induced means to increase precipitation. It can only be done in certain circumstances, if there is an excess of water vapour in clouds in the atmosphere which can be seeded to provide nuclei around which water droplets can condense. There is no evidence that it can produce a long-term increase in precipitation, but it is used in many countries to increase winter precipitation.
- Conservation is an alternative approach to extending water resources, either by greater efficiency in using water, by recycling, by substitution, or by changing practices.