Every 5 years the U.S. Geological Survey (USGS) compiles county, state, and national water withdrawal and use data for a number of water-use categories. These five categories covered the major human water uses. In 2005, about 410,000 million gallons per day of water was withdrawn for use in the United States. About 80 percent of the total withdrawal was from surface water, of which 82 percent was freshwater. The remaining 20 percent of total withdrawals was from groundwater, of which about 96 percent was freshwater.

This image shows 2005 data of human water use percentages for the various categories. Thermoelectric power and Irrigation top the list, with domestic and public water use the third source of water withdrawal for the US. (EPA, 2005)

Throughout the world, irrigation (water for agriculture, or growing crops) is probably the most important use of water. Almost 60 percent of all the world's freshwater withdrawals go towards irrigation uses. Large-scale farming could not provide food for the world's large populations without the irrigation of crops.

In the US, irrigation has represented about 65 percent of total withdrawals, since 1950. Withdrawals for irrigation increased by more than 68 percent from 1950 to 1980. Withdrawals have decreased since 1980 and have stabilized. Depending on the geographic area of the United States, this overall decrease can be attributed to climate, crop type, advances in irrigation efficiency, and higher energy costs.

Production of electrical power results in one of the largest uses of water in the United States and worldwide. Water for thermoelectric power is used in generating electricity with steam-driven turbine generators. In 2005, about 201,000 million gallons of water each day were used to produce electricity. Surface water was the source for more than 99 percent of total thermoelectric-power withdrawals. In coastal areas, the use of saline water instead of freshwater expands the overall available water supply. Thermoelectric-power withdrawals accounted for 49 percent of total water use, 41 percent of total freshwater withdrawals for all categories, and 53 percent of fresh surface-water withdrawals. (USGS, 2005)

The industries that produce metals, wood and paper products, chemicals, gasoline and oils are major users of water. Probably every manufactured product uses water during some part of the production process. Industrial water use includes water used for such purposes as fabricating, processing, washing, diluting, cooling, or transporting a product; incorporating water into a product; or for sanitation needs within the manufacturing facility. Some industries that use large amounts of water produce such commodities as food, paper, chemicals, refined petroleum, or primary metals. Most industrial water is returned to the system, however the concern is about the quality of the industrial water returning to the system.

Industrial withdrawals were about 4 percent of Nation's total withdrawals and about 9 percent of total withdrawals for all categories excluding thermoelectric power. Surface water was the source for 83 percent of total industrial withdrawals, whereas groundwater accounted for about 17 percent of withdrawals. Nearly all (92 percent) of the surface-water withdrawals and (99 percent) of the groundwater withdrawals for industrial use were freshwater.

Fish farming is only one aspect of aquaculture. Aquaculture water use is water associated with raising creatures that live in water, such as shellfish for food, restoration, conservation, or sport. In many lakes, rivers, and reservoirs around the country, recreational fishermen enjoy catching fish that have been raised in fish ponds and released to natural waters. Aquaculture production occurs under controlled feeding, sanitation, and harvesting procedures primarily in ponds, cages, net pens, and closed recirculation tanks.

Public supply represents about 13 percent of total freshwater withdrawals, and 21 percent of all withdrawals, not including thermoelectric power. Public water-supply systems, which you might know better as the county and city water departments, are vitally important to all populations. These are government or privately-run facilities that withdraw water from rivers, lakes, reservoirs, and wells and then deliver it to our homes, businesses, and schools. The majority of the population (about 86 percent) of the United States get their water in this manner. You probably get your home drinking water this way.

Domestic water use is water used for indoor and outdoor household purposes— all the things you do at home: drinking, preparing food, bathing, washing clothes and dishes, brushing your teeth, watering the yard and garden, and even washing the dog.

Water quality can be thought of as a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics.

Most of the color in water you see around you comes from suspended material. The picture on this slide shows a rive with highly-turbid water containing suspended sediment. Algae and suspended sediment particles are very common particulate matter that cause natural waters to become colored.

If you scoop up some muddy river water in a glass you are viewing the suspended sediment in the water. If you leave your glass in a quiet spot for a while the sediment will start to settle to the bottom of the glass. The same thing happens in rivers in spots where the water is not moving so quickly—much of the suspended sediment falls to the stream bed to become bottom sediment (yes, mud). The sediment may build up on the bottom or it may get picked up and suspended again by swift-moving water to move further downstream.

Turbidity is the amount of suspended solids such as clay, algae, silt found in water. High concentrations of particulate matter affect light penetration and productivity, recreational values, and habitat quality, and cause lakes to fill in faster. In streams, increased sedimentation and siltation can occur, which can result in harm to habitat areas for fish and other aquatic life. For this reason, turbidity readings can be used as an indicator of potential pollution in a water body.

Excessive turbidity in drinking water is aesthetically unappealing, and may also represent a health concern. Turbidity can provide food and shelter for pathogens. If not removed, turbidity can promote regrowth of pathogens leading to waterborne disease outbreaks, which have caused significant cases of gastroenteritis throughout the United States and the world.

pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. Since pH can be affected by chemicals in the water, pH is an important indicator of water that is changing chemically. Safe drinking water has a pH range between 6.5-8.5. pH of rivers and streams can vary based on pollution and environmental factors.

Water that is saline contains significant amounts of dissolved salts, the most common being the salt we all know so well—sodium chloride (NaCl). In this case, the concentration is the amount (by weight) of salt in water, as expressed in "parts per million" (ppm). If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts.
Water for human consumption should have less than 500 ppm dissolved salts. Water >2000ppm is unsuitable for drinking, but could be used for cooling. Ocean water contains 35,000ppm of dissolved salts.

The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water. Many industrial and domestic water users are concerned about the hardness of their water. When hard water is heated, such as in a home water heater, solid deposits of calcium carbonate can form. This scale can reduce the life of equipment, raise the costs of heating the water, lower the efficiency of electric water heaters, and clog pipes. But hard water can have some benefits, too. Humans need minerals to stay healthy, and the National Research Council (National Academy of Sciences) states that hard drinking water generally contributes a small amount toward total calcium and magnesium human dietary needs.

Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water - DO can tell us a lot about water quality. Rapidly moving water, such as streams tends to contain a lot of dissolved oxygen, whereas stagnant water contains less. Bacteria in water can consume oxygen as organic matter decays. Thus, excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen-deficient situation that can cause a water body and aquatic life "to die."