Water Resources of the United States

What is water quality? To most students, water quality may suggest only "clean" water for drinking, swimming, and fishing. But to the farmer or manufacturer, water quality may have an entirely different meaning. One of the most important issues concerning the quality of water is how that water will be used. Water that is perfectly fine for irrigation might not be suitable for drinking or swimming.

The quality of water can change as it flows over the land surface as rivers, streams, lakes, or ponds (surface water), or under the land surface (ground water). Because surface and ground waters are interconnected in some areas, changes in the quality of surface water can affect the quality of the area's ground water, and vice versa. These changes in water quality may be due to natural factors or human activities.

As rock minerals come in contact with water, some dissolve and become part of the surface- or ground-water system. Other natural materials, such as soil or organic matter, become suspended in the water and move from one place to another. The effects of human activities on water may result from land disturbances, which increase the amount of rock minerals, soils, or organic matter available to be transported by and dissolved in water, or from the addition of human-made pollutants. When water is degraded to a point that affects its use for a particular purpose, it has become polluted.

Water pollution originates from two very different sources: point sources and nonpoint sources. This poster depicts human activities associated with point sources (labeled in yellow) and nonpoint sources (labeled in red). Also displayed is the movement of pollutants from their sources to surface and ground waters. The stream flowing from the mountains on the left-hand side of the poster represents clean water not affected by human activities. The river on the left-hand side of the poster receives pollutants from point sources (wastewater treatment plant, storm drain, and factory). The quantities of pollutants entering this river are reduced as a result of pollution-control measures. The river on the right-hand side of the poster receives pollutants from many nonpoint sources (suburban lawn, parking lot, construction site, landfill, logging area, septic tank, and agricultural field). This river receives large amounts of pollution because there are no pollution controls. The bottom part of the poster displays the movement of water between streams and the underlying aquifer. The poster is folded into 8.5" x 11" panels; the front and back sides caneasily be photocopied.

Point-Source Pollution

Pollution contributed to water from a discrete source, such as a pipe, ditch, tunnel, or well, are referred to as point sources. Generally, pollution from point sources are controlled to some degree by treatment technology. Municipal wastewater treatment plants are one of the most common examples of treatment of point sources. While a municipal wastewater treatment plant might receive water from many sources, it discharges into a water body at a single point.