“Well water” is not one thing. Your well’s safety depends on the local rock, how the well was built, what is around it and your plumbing, so two neighbors can have very different results.

Who is responsible for well water safety?

You are. According to the EPA, about 15% of the U.S. population, over 43 million people, rely on private wells. The EPA states that the quality of water from private domestic wells is not regulated by the federal government under the Safe Drinking Water Act, nor by most state governments.

The CDC puts it plainly: government officials do not regulate, treat or monitor tap water from private wells, and as a well owner “you are responsible for testing your well to make sure the water is safe to drink.”

That is the biggest difference from city water: with a well, nobody checks unless you do.

Is well water safe to drink? What national data shows

Usually, but not as often as most owners assume. In a USGS study of about 2,100 private wells across the country, roughly 23% had at least one contaminant at a level of potential health concern (the EPA summarizes this as about one in five wells).

Most of those problems were natural, not pollution. The USGS found that radon, arsenic, uranium and manganese came from the rock the aquifer flows through. Nitrate was the main exception, coming mostly from septic systems and fertilizer. The USGS also notes that contaminants often show up together as mixtures, not one at a time.

The main risks in well water

This table covers the contaminants most likely to make well water unsafe to drink. Limits are EPA standards or health advisories for public water, which are the best yardsticks for a private well.

Contaminant	Limit or guideline	Where it is more common	Our guide
Total coliform / E. coli	Should be absent	Shallow wells, sandy soil, wells near septic systems or animals, after flooding	Coliform bacteria
Nitrate	10 mg/L as nitrate-nitrogen	Agricultural areas; near septic systems	Nitrate
Arsenic	10 ppb (µg/L)	Natural geology; the USGS highlights the Southwest, the glacial aquifers of the northern U.S. and parts of the East	Arsenic
Lead	Health goal of zero; action level 15 ppb	Older plumbing and acidic (low pH) water	Lead
PFAS (PFOA and PFOS)	4.0 parts per trillion each	Near sites where PFAS were released	PFAS
Manganese	0.3 mg/L health advisory	Natural geology; often found with iron	Manganese
Uranium	30 µg/L	Natural geology, varies by region	Testing guide
Radon (in water)	No federal standard	Crystalline rock aquifers in the Northeast, the central and southern Appalachians and parts of Colorado (USGS)	Testing guide

A few notes on these numbers:

• Bacteria are the most immediate risk. A positive E. coli result means fecal contamination and water that is not safe to drink until treated.
• Nitrate matters most for infants under 6 months, especially when water is used to mix formula.
• Arsenic, uranium and PFAS are long-term risks from years of drinking, not a single glass.
• PFAS rules are in flux. The EPA set limits for six PFAS in April 2024. In May 2026 it proposed keeping the 4.0 ppt limits for PFOA and PFOS, extending the deadline for public systems to April 2031, and rescinding the limits for PFHxS, PFNA, GenX and a PFAS mixture. For a private well, the 4.0 ppt figures remain a reasonable yardstick; check your state, since some set their own limits.
• Radon in water mostly matters because it escapes into indoor air. UMass Amherst notes that breathing radon is the main risk, and drinking it is a smaller one. Standards vary by state.

What the CDC recommends testing every year

The CDC and EPA agree on a baseline annual test:

Annual test	Why it matters
Total coliform bacteria	Shows whether surface water or contamination is reaching the well
Nitrate	Flags fertilizer, manure or septic influence; critical for infants
pH	Low pH water can corrode plumbing and release lead and copper
Total dissolved solids (TDS)	A general check on mineral content that can reveal changes over time

This baseline does not include arsenic, lead, PFAS, uranium or radon. Your county or state health department can tell you which of these are common where you live. Our well water testing guide lists which add-on tests fit which situations.

Always use a state-certified lab. Home strips are fine for quick checks of pH or hardness, but not for health decisions. See how to test well water at home for how to collect a sample properly.

When to test your well beyond the yearly check

The CDC recommends testing again, or testing for more, when:

• There is flooding or land disturbance near your well. See well water after a flood.
• You replace or repair any part of the well system.
• You notice a change in taste, color or smell.
• Someone in the home becomes pregnant, or a child starts living with you.
• You hear about well water problems in your area.

The EPA adds new construction near the well to that list. Test a well before you drink from it if you are moving into a new home; our guide to buying a home with a well covers what to ask for before closing.

Signs you should not rely on

Many owners judge their water by how it looks, smells and tastes. That catches nuisance problems but misses many of the dangerous ones.

• Clear water can be unsafe. Arsenic has no taste, smell or color, according to Penn State Extension. The EPA says the same about lead.
• Good taste proves nothing. The EPA notes that some contaminants give no sensory warning at all, which is why its testing advice is based on what is near your well, not on how the water seems.
• “We’ve drunk it for years” is not a test. Levels can change with seasons, land use and well condition.
• A neighbor’s clean result is not yours. Wells a short distance apart can differ, especially for arsenic.
• Bad taste is not always dangerous. Iron, a rotten egg smell or a metallic taste are often nuisance problems, although they are still worth testing.

Can you drink well water without a filter?

Yes, if your test results are within limits. Buying a filter “just in case” can waste money and give false confidence, because no single filter removes everything.

Boiling is not a cure-all either. A rolling boil for at least one minute kills bacteria, but it does not remove chemical contaminants. Penn State Extension warns that boiling concentrates nitrate as water evaporates, and the Ohio Department of Health states that boiling does not remove arsenic.

How to make well water safe to drink

Match the treatment to the problem your test finds.

Test result	Usual approach	Learn more
Coliform or E. coli present	Find and fix the entry point, shock chlorinate, retest; UV or chlorination if it keeps coming back	How to shock a well, UV treatment
Nitrate above 10 mg/L	Reverse osmosis at the kitchen tap, ion exchange or distillation; bottled water for infants meanwhile	Nitrate
Arsenic above 10 ppb	Reverse osmosis or adsorptive media, often with an oxidation step	Arsenic
Lead or copper, low pH	Neutralize pH at the point of entry; point-of-use filter certified for lead	Well water pH, Lead
PFAS detected	Treatment certified for the specific PFAS found	PFAS

A few rules of thumb:

1. Fix the well before you treat the water. A cracked cap or casing lets contamination back in, whatever equipment you install.
2. Choose certified equipment. Look for a system certified to reduce the specific contaminant on your report.
3. Point of use or whole house? For contaminants that matter only when swallowed, such as nitrate or arsenic, a system at the kitchen sink is often enough. Bacteria are usually treated for the whole house, since you also brush teeth and wash dishes with that water. See reverse osmosis for well water.
4. Retest after installation, and keep up with maintenance. Treatment only works while it is maintained.

Who is at higher risk from well water?

Some people are more sensitive to contaminants. The EPA suggests testing more often if small children, older adults, pregnant or nursing household members live in the home. In particular:

• Infants under 6 months: most at risk from nitrate, and more sensitive to manganese. Do not mix formula with well water until it has been tested.
• Pregnant people: the CDC lists pregnancy as a reason to retest, and nitrate and lead are key concerns.
• Young children: the EPA says children are affected by lead at lower levels than adults.
• Older adults and anyone with a weakened immune system: more vulnerable to waterborne germs. Ask your doctor whether extra precautions make sense.

Frequently asked questions

Is well water safer than city water?

Neither is automatically safer. City water is treated and tested under federal rules; well water is tested only if you do it. A well that is tested and maintained can be as safe as city water.

Is well water safe for babies?

Only after testing. Nitrate above 10 mg/L as nitrate-nitrogen is dangerous for infants, and boiling makes it worse. Use bottled water for formula until you have a clean certified lab result for at least bacteria and nitrate.

How do I know if my well water is contaminated?

You usually can’t tell by looking; a certified lab test is the only reliable way. A new smell, color change or illness in the household is a reason to test right away, but no signs does not mean safe.

Can well water make you sick?

Yes. Bacteria and other germs can cause stomach illness within days, while contaminants like arsenic, nitrate and lead cause problems over time. That is why the CDC recommends yearly testing.

How much does it cost to test well water?

It varies by lab and panel. Ask your county health department; some test private wells for free.

Related guides

• Well water testing: what to test for and how often
• How to test well water at home (and when you need a lab)
• Coliform bacteria in well water: what a positive test means

Sources

• CDC – Guidelines for Testing Well Water
• U.S. EPA – Private Drinking Water Wells
• USGS – Contamination in U.S. Private Wells
• U.S. EPA – Proposed PFOA and PFOS Compliance Extension Rule

This guide is for general information. Have your water tested by a state-certified lab, and follow your local health department’s advice if a test shows a problem.