Uses of fresh water can be categorized as consumptive and non – consumptive sometimes called “Renewable”. Use of water is consumptive if that water is not immediately available for another use. Losses to sub – surface seepage and evaporation are considered consumptive, as water is incorporated into a product (such as farm produce). Water that can be treated and returned as surface water, such as sewage, is generally considered non – consumptive if that water can be put to additional use.
It is estimated that 69% of world – wide water is used for irrigation, with 15 – 35% of irrigation withdrawals being unsustainable.
In some areas of the world, irrigation is necessary to grow any crop at all, in other areas it permits more profitable crops to be grown or enhances crop yield. Various irrigation methods involve different trade – offs between crop yield, water consumption and capital cost of equipment and structures.
It is estimated that 15% of world – wide water user is industrial users include power plants, which use water for cooling or as a power source (i.e. hydroelectric plants), ore and oil refineries use water in chemical processes and manufacturing plants use water as a solvent.
The portion of industrial water usage that is consumptive varies widely, but as a whole is lower than agricultural use.
It is estimated that 15% of world – wide water use is for household purposes. These include drinking water, bathing, cooking, sanitation and gardening. Basic household water requirements have been estimated by Peter Gleick at around 50 liters per person per day, excluding water for gardens.
Recreational water use is usually a very small but growing percentage of total water use. Recreational water use is mostly tied to reservoirs. If a reservoir is kept full or than it would otherwise be for recreation, then the water retained could be categorized as recreational usage. Release of water from a few reservoirs is also timed to enhance water boating, which also could be considered as recreational usage. Other examples are skiers, nature enthusiasts and swimmers.
- Environmental Use:
Explicit environmental water is also a very small but growing percentage of total water use. Environmental water usage includes artificial wetlands, artificial lakes intended to create wildlife habitat, fish ladders around dams and water releases from reservoirs timed to help spawn.
For example: water release from a reservoir to help fish spawn may not be available to farms upstream.
Much of the fresh water used arrives as the result of precipitation that does not seep into the ground or does not return to the atmosphere by evaporation or transpiration, is called surface water. It forms streams, lakes, wetlands and artificial reservoirs. Watersheds drain water into bodies of surface water.
Surface water is naturally replenished by precipitation and naturally lost through discharge to evaporation and sub-surface seepage into the groundwater. Although there are other sources of groundwater, such as connate water and magmatic water, precipitation is the major one and groundwater originated in this way is called meteoric water.
Scientists estimate that groundwater makes up 95% of all freshwater available for drinking. Groundwater is a significant source of water for many municipal water systems in the United States. Rural residents, withdrawing their water from wells, also rely upon groundwater.
Each source of water has a unique set of contaminants; groundwater stores pesticide chemicals and nitrate while surface water contains most bacteria and other microorganisms. Because of the interconnectedness of groundwater and surface water, these contaminants may be shared between the two sources. Neither water source can ever be entirely free from water contaminants. Due to the cycle of water (hydrology), the two sources of drinking water feed each other, sharing contaminants