Germs
As water moves down through layers of soil, disease-causing germs such as bacteria and viruses are filtered out. For this reason, groundwater often produces drinking water that does not need to have chlorine added to kill germs.
Wells close to streams or lakes might not produce germ-free water. These wells are said to be under the direct influence of surface water. Water from these wells might not pass through very much soil as it moves from surface water to the well. Without the filtering of soil, germs from the surface water might be present in the well water.
Some wells are not constructed properly and allow germs to enter groundwater from the well itself. This is not a natural characteristic of groundwater and is discussed in more detail under Wells in the section on Protecting Groundwater from Contamination.
Minerals
Groundwater varies greatly in the minerals it contains. These minerals are dissolved from the rocks of the aquifer. Generally, the longer water has been underground, the more natural minerals it contains. You can predict the type of rocks the groundwater flowed through during its time underground by the minerals in the water.
A small amount of minerals in water gives it a pleasant taste. In excess, natural minerals can be a nuisance, but most are not a health problem In Oregon, one exception in arsenic.
In a few parts of Oregon, arsenic has been found in groundwater above safe levels for drinking water. While arsenic can be a contaminant from human activity, the arsenic in Oregon appears to be naturally dissolved from the rocks in the aquifers. If you have a private well and are concerned about arsenic, contact a local water testing lab. (Download a list of drinking water labs or contact the Oregon Health Division at 503-731-4317.) Also see the USGS report Arsenic in Ground Water in the Willamette Basin, Oregon.
Common minerals in Oregon's groundwater:
- Iron--water turns orange, stains the laundry and bathroom fixtures, may taste like metal.
- Calcium & magnesium--causes "hard water" and leaves chalky white deposits.
Another natural material in groundwater:
- Hydrogen sulfide gas--smells like eggs, produced by a harmless bacteria that lives deep underground, does not stay in water exposed to air.
Water can be treated to remove germs and other materials that may pose a health risk or make the water unpleasant to drink. Contact the OSU Extension Service Well Water Program for information.