The Complete Guide to Testing Your Home Water

Why your water might not be what you think

If your water looks clear and tastes fine, it's easy to assume it's safe. Most contaminants that actually matter for your health are invisible, odorless, and tasteless at the levels that affect you. Lead doesn't change the color of water. Arsenic doesn't have a smell. PFAS — the so-called "forever chemicals" — are completely undetectable to your senses, and they show up in tap water across all 50 states.

Public water utilities are required to publish an annual Consumer Confidence Report (CCR) showing what they tested for and what they found at the treatment plant. That report tells you what was in the water when it left the plant. It does not tell you what comes out of your faucet — because the pipes between the plant and your home, and the plumbing inside your walls, can add things the utility never measured.

Private well owners get no report at all. If you have a well, the only person testing your water is you.

City water vs. well water: different risks

Where your water comes from determines what's most likely to be in it. The two systems are tested differently because they fail differently.

On city water, your biggest unknowns are usually disinfection byproducts (THMs and HAA5 form when chlorine reacts with organic matter in pipes), lead and copper from your home's plumbing, and PFAS that the utility may or may not be removing. Your CCR tells you what was at the plant — your faucet is a separate question.

On well water, your biggest unknowns are bacteria (especially total coliform and E. coli), nitrates from agriculture or septic systems, arsenic from the surrounding geology, and heavy metals or radon that can leach in from the ground itself. Wells are also vulnerable to surface contamination after heavy rain or flooding.

The contaminants most worth testing for

There are over 90 contaminants the EPA regulates in drinking water, and hundreds more that aren't regulated. You don't need to test for all of them. The list below covers what we recommend for most U.S. homes, and why each one matters.

Lead: There is no safe level of lead exposure for children, according to the American Academy of Pediatrics. The EPA's current action level is 15 parts per billion (ppb), dropping to 10 ppb under the Lead and Copper Rule Improvements. If your home was built before 1986, lead solder is likely in your plumbing.

PFAS: The EPA finalized the first-ever national drinking water standards for PFAS in April 2024. The limits for PFOA and PFOS are 4 parts per trillion — yes, trillion. These chemicals are linked to immune effects, cholesterol changes, and certain cancers.

Bacteria (total coliform and E. coli): A baseline test for any well, and worth doing on city water if you've ever had a back-siphon event or a pressure loss. E. coli specifically indicates fecal contamination and requires immediate action.

Nitrates: The EPA limit is 10 mg/L (as nitrogen). The most acute concern is methemoglobinemia ("blue baby syndrome") in infants under six months. Pregnant people are also at higher risk.

Arsenic: A naturally occurring heavy metal that affects an estimated 2 million U.S. private wells. EPA limit is 10 ppb. Long-term low-dose exposure is the concern — there are no acute symptoms.

Radon: A radioactive gas that can enter homes from soil — and also from well water. The EPA action level for indoor air is 4 pCi/L. Radon is the second-leading cause of lung cancer in the United States.

VOCs: Volatile organic compounds include solvents, gasoline components, and degreasers. They can appear in both water and air, often near gas stations, dry cleaners, or industrial sites.

How labs actually detect contaminants at parts-per-billion

A part per billion is roughly one drop in an Olympic swimming pool. A part per trillion — the unit used for PFAS — is one drop in a thousand swimming pools. Detecting things at those concentrations requires instruments most people have never heard of.

For metals like lead, arsenic, and copper, labs use ICP-MS (inductively coupled plasma mass spectrometry). The water sample is heated to about 10,000 degrees Kelvin — hotter than the surface of the sun — turning every atom into ions that get sorted by mass. The instrument can detect a single lead atom in a billion water molecules.

For organic chemicals like PFAS, VOCs, and pesticides, labs use gas chromatography or liquid chromatography paired with mass spectrometry (GC-MS or LC-MS/MS). The chromatograph separates the chemicals one by one, and the mass spec identifies each by its molecular fingerprint.

Bacteria are tested differently. Most labs use a method called Colilert or membrane filtration — the sample is incubated for 18 to 24 hours and color-changing reactions reveal whether coliform or E. coli are present.

The takeaway: a real lab result is not a guess. It's an instrument reading with a defined detection limit and a documented uncertainty. That's why "lab-backed" matters.

How to read your lab report

Every lab report has four pieces of information you need to find: the parameter (what was tested), the result (how much was found), the units (ppb, ppm, mg/L), and the limit (the EPA MCL, action level, or health-based guideline).

Pay attention to the units. "5 mg/L" is a thousand times larger than "5 µg/L" (which is the same as 5 ppb). Mixing them up is the most common mistake people make reading their own report.

If a result is below the lab's detection limit, you'll typically see "<" followed by a number — that means the contaminant wasn't detected at or above that limit. It doesn't mean zero, but it means the lab couldn't measure it.

Compare each result to the EPA MCL (Maximum Contaminant Level) or the EPA action level. Anything at or above those numbers requires action. For some contaminants — like lead and PFAS — the health-based goal (MCLG) is zero, even if the enforceable limit is higher.

Choosing the right filtration

Once you have results, filtration is a downstream decision — and you can't pick the right filter without knowing what you're trying to remove. "Best water filter" is not a real category. "Best filter for lead" or "best filter for PFAS" is.

Activated carbon filters (the most common pitcher and faucet-mount filters) remove chlorine, taste, odor, many VOCs, and — if certified to NSF/ANSI 53 — lead. They do not effectively remove arsenic, nitrates, or most dissolved minerals.

Reverse osmosis (RO) systems remove the broadest range of contaminants: lead, arsenic, nitrates, fluoride, PFAS, and dissolved solids. They produce a few gallons of wastewater per gallon of clean water, and they're typically installed under the sink for drinking water only.

Ion exchange (water softeners, but also specialized resins) removes hardness, some heavy metals, and nitrates. UV systems kill bacteria but don't remove chemicals. Whole-house systems treat all water entering the home; point-of-use systems treat one tap.

A testing schedule you can actually keep

For private wells, test annually for total coliform bacteria, nitrate, nitrite, pH, and total dissolved solids. Test every three years for heavy metals (lead, arsenic, copper) and VOCs. Test once for radon in water if you've never done so, and once for PFAS — and re-test if your area has known industrial or military sources.

For city water, you can rely on the CCR for source water quality, but test your tap at least once for lead and copper (especially if your home is pre-1986), once for PFAS, and once for disinfection byproducts. Re-test any time your CCR shows a violation, you have plumbing work done, or your taste or color changes.

After a flood, leak, or pressure loss, test for bacteria as soon as the water clears. Don't trust visual recovery.