A clean, constant supply of drinking water is essential to everyone. People in large cities frequently drink water that comes from surface water sources, such as lakes, rivers, and reservoirs. These sources of water can be close to the community, or many miles away. In either case, when you think about where your drinking water comes from, it's important to consider not just the river or lake that you can see, but the entire watershed. The watershed is the land area over which water flows into rivers, lakes, or reservoirs.

In South Dakota water is supplied by surface and subsurface sources. Water uses include drinking, irrigation, agriculture, industry, recreation, wastewater treatment, power generation, and mining. (See how South Dakota ranks nationally in these 1990 water-use maps.)

Quality drinking water is vital to the growth and prosperity of cities, towns and in rural areas. Drinking water is readily available through municipal or rural water systems in most areas of the state. In the last 20 years, rural water systems (map) have provided a sufficient water source in areas where water is not readily available.

Eastern South Dakota has an extensive aquifer system that can be as shallow as 2 feet or as deep as a few hundred feet. In western South Dakota, the accessibility of the groundwater is not as good. Most residents get their water supply from one of these aquifers via wells.

Wells can be as deep as three thousand feet and often the water quality is marginal. These wells tap into the natural reservoirs under the earth's surface that may be only a few miles wide, or may span the borders of many states.

The largest amounts of groundwater are withdrawn from the shallow Big Sioux aquifer in eastern South Dakota and from the Madison and Minnelusa aquifers in the Black Hills. As with surface water, it is important to remember that activities many miles away from you may affect the quality of groundwater.