How Often Should You Test Well Water?

Updated August 2026 · ClearTap editorial · Topic: private well testing schedule

A neighbor mentions over the fence that her well came back positive for coliform after the spring rains. You go looking for your own paperwork and find one sheet from the closing — six years ago, two lines on it, both marked "pass." Your water is clear, it tastes the same as it did in March, nobody has been sick. None of that is evidence. Coliform, nitrate and arsenic are colorless and tasteless, which is exactly why the schedule exists.

The core answer: test a private well at least once a year for total coliform bacteria, nitrate, total dissolved solids and pH — the baseline CDC and EPA give every well owner, at $20–75 through a state-certified lab. Add a broader panel — arsenic, lead, uranium, radon, fluoride, manganese, VOCs — every 3–5 years or once at purchase, at $150–400. Then test off-schedule whenever something changes: flooding over the wellhead, any repair that opens the well or pump, a new taste or color, a bad result next door, or a pregnancy or infant in the house, where nitrate above 10 mg/L is the specific concern. EPA does not regulate private wells — nobody samples your water but you.

Reviewed by the ClearTap editorial team. We publish plain specs, model compatibility and NSF/EPA-based standards so you can judge for yourself — no lab-test theatre and no upsell. We do not run a water lab; our guidance is built from published specifications and NSF/EPA standards, not invented tests. General information about water quality only, not medical or drinking-water advice: for legal or health decisions about your water, test it with a certified laboratory.

Before you order anything: read the last report you already have

Most well owners have had water tested at some point and have no idea what was covered. Find the sheet and read three things off it.

1. The parameter list, not the verdict. A real-estate closing test in most states is two analytes: total coliform and nitrate. "Passed" says nothing about arsenic, uranium, radon, lead or manganese — none were in the bottle. Count the rows: two to four is a mortgage test, a real well panel runs 12–20 rows.

2. The date and the season. Bacteria and nitrate move with the water table, so a sample pulled in a dry August can come back clean from a well that goes positive every April after snowmelt. If every test you own was taken in late summer, you have never tested your worst case.

3. The units. Nitrate is reported two ways — as nitrogen (NO₃-N) or as nitrate ion — and the numbers differ by a factor of about 4.4. EPA's limit of 10 mg/L is as nitrogen, so 20 mg/L "as nitrate" is about 4.5 as N and passes, while 20 as N is double the limit.

The schedule: what to test, how often, what it costs

The annual four are cheap, and many county health departments hand out coliform-and-nitrate bottles free or at $10–25.

Test	How often	What it catches	Typical cost
Total coliform + E. coli	Every year, plus after any well work	Surface water reaching the aquifer, or a failed seal; EPA's goal is zero	$20–40
Nitrate / nitrite	Every year; twice a year with an infant or pregnancy in the house	Septic and fertilizer influence; EPA MCL 10 mg/L as N, nitrite 1 mg/L	$15–35
pH + total dissolved solids	Every year	Corrosive water leaching copper and lead from your own plumbing; EPA secondary pH 6.5–8.5, TDS 500 mg/L	Bundled, $10–25
Arsenic, uranium, radon, fluoride	Every 3–5 years, or once if local geology is known for them	Bedrock contaminants, no taste or color; arsenic MCL 10 ppb, uranium 30 µg/L, fluoride 4.0 mg/L	$25–75 each
Lead + copper	Every 3–5 years, and after plumbing work	Solder, brass fittings, pump parts — not the aquifer; EPA action level 15 ppb	$25–50
Iron, manganese, hardness, sulfate	Every 3 years, or when staining or odor starts	Stains and equipment damage; secondary standards iron 0.3 mg/L, manganese 0.05 mg/L	$40–80 grouped
Full panel (VOCs, pesticides, metals)	Once at purchase; repeat if nearby land use changes	Fuel tanks, dry cleaners, farm chemicals, industrial history	$250–600

The calendar is only half of it. These events reset the clock regardless of when you last tested.

What happened	Test for	How soon
Flooding over or near the wellhead	Coliform and E. coli	Once water recedes; unsafe to drink until clean
New pump, pulled pipe, new cap, shock chlorination	Coliform and E. coli	1–2 weeks after, once chlorine has flushed
New taste, smell, color or cloudiness	Coliform, nitrate, iron, manganese, sulfate	Now — don't wait for the annual date
A neighbor's well tests positive	The same analyte they found	Within weeks; you likely share an aquifer
Pregnancy, or an infant under six months	Nitrate, specifically	Before the baby comes home, then annually
Repeat unexplained gastrointestinal illness	Coliform and E. coli	Now, alongside a call to your doctor
Buying or selling the house	Coliform and nitrate; lenders often require it	During inspection

Sampling method is per analyte, not per trip. Bacteria bottles have a holding time — labs generally need them back within 24–30 hours, chilled near 40 °F (4 °C), so collect on a weekday morning, never Friday night. Lead is sampled first-draw: cold water, aerator off, after the plumbing has sat unused 6–8 hours, because the point is what the pipes gave up overnight. For a certified lab, ask your county health department or EPA's Safe Drinking Water Hotline at 800-426-4791.

Why treatment equipment doesn't get you off the schedule

The common turn is to spend $1,500–4,000 on a whole-house system and quietly stop testing. Equipment makes testing more necessary, for three reasons.

Nothing treats everything. A UV lamp certified to NSF/ANSI 55 inactivates bacteria and does nothing to nitrate, arsenic or lead. Whole-house carbon certified to NSF/ANSI 42 improves taste and doesn't touch nitrate. An under-sink RO unit certified to NSF/ANSI 58 handles arsenic and nitrate at one faucet, while every other tap runs untreated.

Equipment degrades invisibly. UV lamps lose output long before they go dark and are rated for roughly 9,000–12,000 hours — about a year of continuous run — while the quartz sleeve fouls with iron and cuts the dose further. RO membranes fail gradually; resin and iron media lose capacity the same quiet way.

You need a before and an after. Raw-water numbers are what size the equipment — iron above 0.3 mg/L or hardness above 10 gpg changes which system is appropriate — and a post-commissioning sample is proof it works rather than a receipt. Without the pair, a failing system looks exactly like a working one.

The stopgap people reach for has the same blind spot. Boiling handles bacteria and nothing else — it drives off water as steam and leaves nitrate, arsenic, lead and uranium behind at a higher concentration than you started with. While a result on any of those is pending, the answer is bottled water, not the kettle.

We don't operate a water lab. The schedule and limits here come from published guidance: CDC's private-well testing recommendations, EPA's private drinking water well pages, its National Primary Drinking Water Regulations (nitrate 10 mg/L as N, arsenic 10 ppb, uranium 30 µg/L, lead action level 15 ppb) and Secondary Drinking Water Standards (iron 0.3 mg/L, manganese 0.05 mg/L, TDS 500 mg/L, pH 6.5–8.5), plus NSF/ANSI 42, 55 and 58 and state health department fee schedules. We have not sampled anyone's well — no article substitutes for a certified laboratory result on your water.

Common mistakes

Treating clear water as evidence. Coliform, nitrate, arsenic, radon and uranium stay invisible and tasteless well above their limits. Looking fine is the normal condition of a well that fails its annual test.
Assuming the closing test covered the well. A mortgage test is usually coliform and nitrate only — two rows out of a 12–20 row panel, silent on the arsenic or manganese a broader test is meant to catch.
Sampling only in the dry season. Bacteria and nitrate peak with snowmelt and heavy rain, so testing every August for a decade can miss a well that goes positive every spring.
Letting the bottle sit over a weekend. Bacteria results are valid only inside a 24–30 hour chilled window. Collected Friday evening, delivered Monday, a sample gets rejected — or reported from an overgrown bottle.

FAQ

How often should you test well water?

At least once a year for total coliform, nitrate, TDS and pH — the CDC and EPA baseline for any private well, at roughly $20–75. Add a wider panel covering arsenic, lead, uranium and radon every 3–5 years, plus an off-schedule test after flooding or well repairs.

Does the EPA test private wells?

No. The Safe Drinking Water Act covers public systems — those serving at least 25 people or 15 connections — and private wells fall outside it entirely. No agency samples your well or notifies you of a problem, which is why a fixed annual date matters.

What should I test for after a flood?

Total coliform and E. coli first: floodwater over the wellhead is the direct route for bacteria. Treat the well as unsafe to drink until a clean result comes back, and retest 1–2 weeks after any shock chlorination so residual chlorine doesn't mask the sample.

Do I still need to test if I have a filter or UV system?

Yes, and arguably more often. UV certified to NSF/ANSI 55 inactivates bacteria but does nothing for nitrate or arsenic, and lamps are rated for only about 9,000–12,000 hours. An annual post-treatment sample is the one way to confirm the system still performs.

Related:

General information about home water quality and testing, based on published CDC and EPA guidance and NSF/ANSI standards — not medical advice, and not a substitute for a laboratory result. Bacteria, nitrate, lead and arsenic can only be measured by a state-certified laboratory; questions about health effects belong with your doctor or state health department. Fees, required parameters and real-estate testing rules vary by state and county.