Frequently Asked Questions


The USGS monitors and studies a wide range of water resources and water conditions, including streamflow, groundwater, water quality, and water use and availability.

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trees and stream
“Reach” can have slightly different meanings, depending on how it is used. A reach is a section of a stream or river along which similar hydrologic conditions exist, such as discharge, depth, area, and slope. It can also be the length of a stream or river (with varying conditions) between two streamgages, or a length of river for which the...
The National Map Hydrography Viewer
Information on the NHD is available on The National Map Hydrography Web page and at the USGS Hydrography Web site.
Water cycle graphic
The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth.
Domestic water use, 2010, by State
Since 1950, the USGS has collected and analyzed water-use data for the United States and its Territories. That data is revised every 5 years. As of 2010, the United States used 355,000 million gallons of water per day (Mgal/d; equivalent to 355 billion gallons per day), or 397,000 thousand acre-feet per year (acre-ft/yr). The three largest water-...
All water on Earth in a sphere, placed over a "dry" globe
The earth is estimated to hold about 1,460,000,000 cubic kilometers of water. The breakdown of where all that water resides is estimated as follows: Oceans (saline) 1,419,120,000 cubic kilometers Ice caps and glaciers (fresh) 31,244,000 cubic kilometers Ground water (fresh and saline) 8,906,000 cubic kilometers Streams and lakes (fresh) 132,860...
Image: Iron Bog near Rochford, SD
The brown stain is from a large amount of iron in your water. It is closely related to simple rust you see on metal, which is iron oxide. The source of the water you use probably is groundwater, and the water has filtered through rocks containing iron-rich minerals on the way to the well.
Glass of water
Once in a while you get a glass of water, and it looks cloudy; maybe milky is a better term. After a few seconds it miraculously clears up! The cloudiness is due to tiny air bubbles in the water. Like any bubbles, the air rises to the top of the water and goes into the air, clearing up the water. The water in the pipes coming into your house might...
Image: Acidifying a Drinking Water Quality Sample for MTBE Analysis
Water is said to be soft if it has a low concentration of calcium and magnesium ions in it, whle hard water has a high concentration of calcium and magnesium. If you use soft water, the ions react with your soap to produce a residue that feels like it is hard to wash off. If you use hard water, you will have a harder time working the soap up into...
Drinking water from tap
The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports are often sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants...
Photo of a young girl drinking water, which likely originated from groundwater sources. 
Bottled water is regulated by the U.S. Food and Drug Administration and by individual states. For general information about bottled water, sources include the International Bottled Water Association and NSF International.
Two USGS National Research Program scientists taking water samples in a wetland.
A frequent cause of musty, earthy odors, especially toward the end of the summer, is naturally occurring organic compounds derived from the decay of plant material in lakes and reservoirs. The odors can be objectionable, but generally are not harmful to health. However, odors can be caused by other constituents as well, so you may want to call...
Image: Natural Iron-rich Acidic Spring Flowing into Cement Creek
Your water might be affected by iron, a commonly occurring constituent of drinking water. Iron tends to add a rusty, reddish brown (or sometimes yellow) color to water, and leaves particles of the same color. If the color is more like black, it could be a combination of iron and manganese. Both of these metals can cause staining of plumbing...