How Impurities Occur in Water

Water makes up 75% of the Earth’s surface, so why is everyone concerned about finding enough adequate drinking water? The truth is, less than 1% of the Earth’s water is fresh water that we can drink. This 1% can become contaminated in a number of ways.

Water can become contaminated right at home. Some older homes have lead pipes or plumbing systems that use lead-based solder to join copper pipes. 
Both can allow lead to leach into drinking water.

Chemicals that are dumped onto or pumped into the ground can easily get into our water supply.

There are an estimated 181,000 industrial waste sites, 13,000 active and inactive municipal landfills.

There are approx. 100,000 ruptured underground gasoline storage tanks in the US that leak substances into our water supplies.

Agricultural pesticides and highway de-icing are among other common practices that can also contaminate water.

Water can become contaminated during its journey from the treatment plant to our homes.

Lead and asbestos cement pipes, prevalent in municipal water distribution systems, can allow harmful substances to leach into the water.

Even chlorine and chloramines used to disinfect our water can react with naturally-occurring organic materials in water, like decaying leaves, and create Trihalomethanes (THMs), which are known to be carcinogenic to lab animals and are suspected to be carcinogenic to humans.


1. Obtain recent water reports
If you live in a large community, contact your water supplier, the local health department, or the state water quality agency to request results of recent water tests. These results will show you the contaminant levels of various substances found in your water.

If you get your drinking water from a private well, your local health department may have information on substance levels and should be able to do some simple testing.

2. Compare test results with MCLs
Compare contaminant levels found in the water with the MCLs set by the EPA to determine if any of the contaminant levels exceed the EPA limits. A current MCL list can be obtained by going to and searching “MCL” or by calling your local EPA office.

3. Research the distribution system
Substance testing is usually done at the treatment plant; however, drinking water can become contaminated after it leaves the plant and makes its journey to your home.