Where we use water

The most obvious and immediate uses occur in its natural setting. They are called instream uses. Fish live in it, as do some birds and animals, at least part of the time. Hydroelectric power generation, shipping, and water-based recreation are other examples of human instream uses.

These instream uses are not always harmless. For example, oil leaking from outboard motors and freighters can cause pollution. Large reservoirs needed for hydroelectric power generation remove water by evaporation and completely change the river regime for downstream users.

The greatest number and variety of water uses occur on the land. These are called withdrawal uses. This term is appropriate because the water is withdrawn from its source (a river, lake or groundwater supply), piped or channelled to many different locations and users, and then is collected again for return to a lake, river or into the ground. Household and industrial uses, thermal and nuclear power generation, irrigation and livestock watering all fall into this category.

Most withdrawal uses "consume" some of the water, meaning less is returned to the source than was taken out. Furthermore, the water which is put back into its natural setting is often degraded. For example, water leaving our houses contains human and household wastes. The same is true of water used in many industrial processes. Often this liquid waste is only partially treated, if at all, before it is returned to nature.

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