Interpreting Water Test Results

What am I looking at on the report?

Most reports list each substance tested, the amount found, the unit of measurement, and a comparison level. The comparison may be a health limit, a limit based on taste or staining, or a note about what the lab can detect. Each of those means something different.

Check first that the report carries your name, address, sample date and the lab name. A mix-up in labeling is rare but possible, and you want to be sure you are reading your own result.

Keep each report in date order so you can compare them. A single result is a snapshot, while several together show whether your water is steady or drifting.

What do the units mean?

Units tell you how much of a substance is in the water. Common ones include milligrams per liter, micrograms per liter and colonies or presence for bacteria. The same number in different units can mean very different amounts, so never compare two reports without checking the units.

If the lab report is hard to read, call and ask them to walk you through it. Labs field these questions all the time.

• Look at the unit beside each number
• Do not compare numbers across reports without matching units
• Ask the lab to explain anything unclear

What is the difference between health limits and aesthetic limits?

Some substances are flagged because they may affect health over time or in a short exposure. Others are flagged because they affect taste, smell, color or staining, or because they cause scale and corrosion in plumbing. Iron and manganese are common examples of the second group, while bacteria and nitrate are often raised as health concerns.

Your state or county health agency can tell you which limits apply and how seriously to take a particular result. The EPA sets national drinking water standards for public systems, and private wells are generally not regulated by them, but those standards are often used as a reference.

Pesticides, metals and natural minerals each have their own reasons for appearing in a report. Local geology often explains a natural mineral result, while land use explains many of the others. A short phone call can save you a lot of worry.

What does a bacteria result mean?

A test that finds coliform bacteria or E. coli does not always mean the water is making people sick, but it does mean something from the surface or from waste may be getting into the supply. Reports often say present or absent rather than giving a number.

If bacteria are found, ask the health department what to do about drinking water right away, and how to find the cause. Possible causes include a damaged cap, a cracked casing, a nearby septic system or flooding. Disinfection steps should come from your health office or a licensed professional, not from guesswork.

When should I retest or get a second opinion?

If a result is surprising or high, retest before you spend money. Samples can be affected by how they were collected. A second sample, sometimes from a different tap, confirms whether the finding is real and steady.

If a number changes sharply between tests, ask what happened between them. Rain, a pump repair, new plumbing or a change in water use can all shift a result.

Do not rely on a quick home test strip for health decisions. Strips can be useful for rough checks, but a certified lab result is what your health office will want to see.

What should I ask before buying treatment equipment?

Treatment should match a specific, confirmed problem. Ask which substance you are treating, what level you are trying to reach, how the device is rated and independently tested, how often it needs service and what it costs to run.

Keep records of every report. Compare future tests against the earlier ones so you can see trends instead of single snapshots.

• Which result am I treating?
• Is the device independently tested for that purpose?
• What maintenance does it need and how often?
• How will I confirm it is working?

Where can I get help understanding my results?

Your county health department is the best first call. Staff see these reports regularly and know the local conditions. State drinking water programs and cooperative extension offices are also good resources, and many publish plain guides for private well owners.

Bring the full report, the sample date and a note of anything that changed recently, such as a repair, a flood or new plumbing. Ask what each flagged item means for drinking, cooking, bathing and for pets and livestock.

If someone in the home has a health concern, ask their doctor too. General education pages cannot replace advice from someone who knows the person.

Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.