Most O'Fallon homeowners have never opened the document that describes their tap water. Public water systems publish an annual water quality report for their customers, often called a Consumer Confidence Report. It is the most direct local source for understanding what is in the water coming into your home. This guide explains how to read it without a chemistry background, and what to do once you have finished.

Find the report for your address

Look for the report on the water provider's website, or ask the provider to mail or email a copy. Reports cover the previous calendar year of testing. Keep the newest one with your home records so you can compare it with later years. Check that the report applies to your address, since some areas are served by different sources or treatment plants.

Start with hardness

Public reports describe O'Fallon tap water as hard. Hardness comes mostly from calcium and magnesium picked up as water moves through rock and soil. It does not describe whether water is safe to drink. It describes how water behaves in pipes and appliances, because hardness is what leaves scale on kettles, shower glass, faucet aerators, and the heating elements of water heaters and dishwashers.

Hardness may appear in the report with its own unit. Check that unit before comparing the figure with a test strip reading, a softener setting, or a result from a lab. Different tools and sources use different units, and mixing them up is a common reason homeowners end up with the wrong softener setting.

Read the disinfection lines carefully

Water systems add chlorine to disinfect water. Chlorine reacts with natural organic material in the source water, which in the O'Fallon area includes material associated with the Missouri River and groundwater. Those reactions produce disinfection byproducts. Reports usually list two groups, TTHM and HAA5, along with a range of results and a running annual average compared against a regulatory standard.

Read the wording closely. A result that stays under the standard is different from a result that is simply listed. Also look for the sampling locations and dates, since results can vary across the distribution system. A byproduct is a compound formed in the water, and the report tells you how the provider measured it, not how it affects any particular person.

Look at the detected items

Local water reports mention radium and arsenic. Both are naturally occurring elements that can be present in source water. A detection is not the same as an exceedance of a standard. Read the detected amount alongside the standard listed next to it, and note whether the report describes the result as within the limit.

If a detected item concerns you, ask the provider which sources and treatment steps apply to your address, and how recent samples were collected. You can also ask whether results are available for the specific water treatment plant that serves your area. Those questions are reasonable for any homeowner and do not require a special reason.

Notice what the report does not cover

The report describes the water leaving the treatment plant and sampled points in the distribution system. It does not describe your home's plumbing, fixtures, or any water softener or filter you have installed. Lead and copper from household plumbing are tested differently, usually at the tap, and they can depend on the age of your pipes and fittings. Water treatment equipment also changes what reaches your faucet, so a clean report does not tell you what comes out of your own system.

Turn the report into a short plan

  • Confirm the report covers your address and note the year it describes.
  • Compare the hardness reading with a test strip or lab result from your own tap, using the same unit.
  • Read the disinfection byproduct lines for their range, running average, and standard.
  • Review each detected item and its listed standard, then write down any questions.
  • Ask the provider about sources, sampling locations, and the treatment plant serving your area.
  • Test your own tap for anything the report does not cover, such as household plumbing metals, through an accredited lab.
  • If you rely on a private well in the area instead, use the Missouri State Public Health Lab for coliform, E. coli, and iron bacteria testing, which is available at free or low cost.

Keep the report, your test results, and any notes together in one folder. When the next report arrives, you will have a baseline for O'Fallon water and a clear list of what to check at home.