- The lead problem is worse than a detection limit. Lead often travels as particles, and the strips that can reach drinking-water levels detect only dissolved lead. A strip can read safe on water carrying dangerous particulate lead.
- Nitrate is the real exception. Strips reach the regulatory level in the right units, which makes a home nitrate check genuinely worth doing, particularly for private wells.
- Most of the error is you, not the strip. In one evaluation, colour-matching by eye reproduced 70 to 75 percent of total variance. Better instructions barely moved it.
What can a strip actually detect, against what the law requires?
This one table is the whole article. Everything else is explanation.
| Contaminant | Regulatory level | What a consumer strip reaches | Verdict |
|---|---|---|---|
| Lead | 15 ppb action level, dropping to 10 ppb on 1 Nov 2027 | 12 of 16 brands tested: 5 to 20 mg/L, roughly 330 to 1,300 times higher | Fails |
| PFOA / PFOS | 4.0 parts per trillion each | No strip exists | Impossible |
| Nitrate | 10 mg/L as nitrogen | Reading steps at 0, 1, 2, 5, 10, 20, 50 in the same units | Works |
| Arsenic | 10 ppb | Purpose-built kit resolves at 10, 30, 50, 70 ppb | Marginal |
| Coliform / E. coli | Presence or absence | Presence or absence kits exist | Not for official use |
| TDS | 500 mg/L, not enforced | Meters measure conductivity accurately | Measures the wrong thing |
Note the units in the lead row, because that is where the scale of the failure hides. The action level is in parts per billion. Most strips detect in milligrams per litre, which is parts per million. Those are a thousand-fold apart, and the strips need several multiples of that before they show anything.
Why can a lead strip say “safe” on dangerous water?
Because of how lead travels, not just how little the strip can see. This is the finding that should change how you think about home lead testing.
The reference work here is Kriss, Pieper, Parks and Edwards, published in Environmental Science & Technology in 2021, from the Virginia Tech group that did the Flint investigations. They tested 16 brands of at-home lead kit. The headline result, in their words:
Most kits (12 of 16 brands) were not suitable for drinking water analysis, with lead detection limits of 5-20 mg/L. Binary strips detected dissolved lead at drinking water-relevant levels but failed to detect particulate lead.
Read that second sentence twice. Some strips can reach drinking-water levels. But they only see lead that is dissolved.
In real plumbing, a great deal of lead arrives as particles: flakes shed from pipe scale, solder and fittings, especially after plumbing work or a change in water chemistry. Those particles are exactly what makes lead dangerous in a tap, and a binary strip does not see them.
The researchers demonstrated this directly. Adding household acids such as lemon juice or vinegar dissolved the particulates enough to push soluble lead above 15 µg/L, at which point the strips could detect it. That is a laboratory trick to prove a point, not a home method. What it proves is that an unmodified strip under-reports real-world lead.
One product claims to work at the regulatory level. SenSafe’s Quick Lead is a lateral-flow test advertised as conforming to the EPA’s 15 ppb guideline in ten minutes. Three things to understand before relying on it: it is a pass or fail at one threshold, not a measurement; we found no independent validation of that claim; and it is set to the current 15 ppb line, which will be misaligned when the level drops to 10 ppb.
Is the lead limit changing?
Yes, and it matters for anyone buying a test today.
The action level is 15 ppb now. Under the EPA’s Lead and Copper Rule Improvements, it drops to 10 ppb on 1 November 2027.
Worth knowing alongside that: lead has a treatment technique rather than a maximum contaminant level, and its health-based goal is zero. There is no amount of lead the EPA considers safe. The action level is a trigger for utility action, not a line below which water is fine.
Can any home kit test for PFAS?
No, and the reason is worth understanding because it applies to every future PFAS product you will see advertised.
The limit for PFOA and PFOS is 4 parts per trillion. Compliance testing uses EPA Methods 537.1 and 533, which means liquid chromatography with tandem mass spectrometry. Colour-change chemistry works in the parts per million range. That is roughly a million-fold gap. It is not a matter of making a better strip.
So every “PFAS home test kit” on the market is a sample collection and shipping kit. You fill a bottle and mail it to a laboratory. There is nothing wrong with that, and it is often the right thing to buy. But it is a mail-in lab service being sold in the packaging of an instant test, and the price reflects the laboratory work rather than the kit.
What about nitrate, where strips actually work?
This is the genuine exception, and it deserves more attention than it gets.
The nitrate limit is 10 mg/L measured as nitrogen. A commonly sold Hach test strip reads in steps of 0, 1, 2, 5, 10, 20 and 50 mg/L as nitrogen. There is a reading step at exactly the regulatory limit, in the same units.
That combination is rare in this category, and it makes home nitrate screening genuinely useful, particularly for private wells near agricultural land where nitrate is the most common real problem.
Two caveats. Read the units on whatever you buy, because nitrate is reported both as nitrogen and as nitrate ion, and the two differ by a factor of about 4.4; a strip reading in the wrong units will mislead badly. And a strip result near the limit should be confirmed by a lab, because nitrate matters most for infants, where the consequences of being wrong are severe.
What are strips genuinely good for?
A short list, and it is shorter than the sixteen pads on the strip suggest.
Before the list, one structural fact: there is no certification standard for consumer water test strips at all. A 2025 evaluation in the Journal of Water and Health put it plainly, describing these kits as unregulated and lacking data on their performance. Hach, which makes serious laboratory instruments, describes its own strips as “semi-quantitative pre-screenings”. That is the manufacturer’s own framing, and it is the right one.
What the evidence supports:
- pH performed best in the evaluations we found: one strip within 0.1 pH units, four of five within 1.0.
- Nitrate, as above, reaches the regulatory level in the correct units.
- Free chlorine is a reasonable use, since the levels of interest are in the parts per million range where this chemistry works.
- Hardness is useful as a rough guide for choosing treatment equipment. Note that hardness has no health-based federal standard, so there is no regulatory line to be accurate against.
The 2025 Journal of Water and Health study also found something important about conditions. Kits performed best in deionised water with no interference, meaning accuracy degrades in real water. Its conclusion was that usefulness depends on which parameter, in which water, with which kit, and for what purpose. That is not a dodge; it is the honest answer.
How much of the error is the strip, and how much is you?
Mostly you, which is the most surprising finding in this research.
A 2024 study from Taylor University tested five 16-in-1 strip products with 80 novice users, validated against atomic absorption spectroscopy. This appeared in an undergraduate research journal, so we treat it as supporting evidence rather than definitive, but its findings are specific and consistent with the peer-reviewed work.
The dominant error source was colour perception. Individual users were self-consistent but differed from each other. A colour-matching survey run with no strips at all reproduced 70 to 75 percent of the total variance in results. Improving the instructions moved the standard deviation only from 0.7 to 0.6.
The same study found copper results that should give any strip user pause: three of five strips reported under 1 ppm for a solution containing 2.5 ppm, and two of five did the same for a 5 ppm solution. Those are false “safe” readings above the strips’ own stated safety thresholds. Iron went undetected between 0 and 5 ppm and registered accurately only at 10 ppm.
The authors’ summary of the problem is the line to remember: colour charts “significantly overestimate the dynamic range the kits are capable of measuring.” The chart implies a precision the chemistry does not have.
What does a TDS meter actually tell you?
Less than almost anyone using one believes.
A TDS meter measures electrical conductivity and multiplies it by a conversion factor to estimate dissolved solids. The factor is not universal: meters typically assume around 0.5 to 0.7, while natural US waters range from about 0.54 to 0.96 depending on what is dissolved in them. So the number on the screen is an estimate of total ionic content, not a measurement of solids.
What it structurally cannot do is identify which ions are present. And that is the whole problem:
- Lead at 15 ppb contributes essentially nothing to conductivity against a background of hundreds of mg/L of calcium and magnesium.
- PFAS at 4 parts per trillion contributes nothing measurable.
- Bacteria are not ionic and do not register at all.
- Most organic compounds are uncharged and invisible to the meter.
It is also worth knowing what TDS is regulatorily. It sits at 500 mg/L as a secondary standard, and the EPA states that it does not enforce secondary maximum contaminant levels, which cover aesthetic effects and are not considered to present a risk to human health.
So a TDS meter is a useful tool for exactly two things: tracking when to change a filter whose job is reducing dissolved solids, and predicting how long a ZeroWater-style cartridge will last. It is not a safety instrument, and a low reading is not a clean bill of health.
When do you actually need a certified lab?
Whenever the result has to convince somebody other than you.
- Property transactions, mortgages and refinancing. Lenders and programmes generally require a certified laboratory result, often with the sample collected by a disinterested third party. Requirements vary by programme and lender, so confirm the specifics with yours rather than with an article.
- Legal disputes. The operative requirement is chain of custody. A home strip has none, and a photograph of a strip proves nothing about which tap it came from or when.
- Public water system compliance. Samples must be analysed by a state-certified laboratory, and for coliform must reach incubation within 30 hours, a deadline a mailed home kit cannot structurally meet.
- Any bacteria result you intend to act on. Both the CDC and EPA direct people to certified laboratories. The CDC’s guidance to private well owners is to use a state-certified laboratory, and it does not mention home kits.
For private wells there is a gap worth naming: they are federally unregulated, so no test is legally required at all. The CDC and EPA recommend annual certified testing for coliform, nitrate, total dissolved solids and pH. Nobody will make you do it.
Where do mail-in kits like Tap Score fit?
In between, and the structure is worth understanding before you buy.
Tap Score is the consumer brand of SimpleLab. SimpleLab is a broker and network rather than a laboratory: it routes your sample to one of a large number of independent laboratories, accredited variously under ISO/IEC 17025, NELAP, state programmes and others.
Does that carry the same standing as a state lab result? It depends on which laboratory ran your sample and who is receiving the result. Accreditation attaches to the laboratory doing the analysis, not to the consumer brand on the box. For a mortgage or a regulatory submission, the receiving body has to accept that specific laboratory’s certification in your state.
If the result is for your own decision-making, this distinction does not matter much and a mail-in panel is a reasonable purchase. If the result has to satisfy a lender, a court or a regulator, ask which laboratory will run it and confirm that body accepts it, before you send the sample.
One sourcing note in fairness: the description of how SimpleLab’s network operates comes substantially from the company’s own materials. We found no independent audit of it.
So what should you actually do?
- Use strips for what they are good at: pH, chlorine, hardness, and nitrate. Treat those as screening, not as measurement.
- Never use a strip to clear lead. A negative result does not rule out particulate lead, and that is the form that matters most in older plumbing.
- Do not buy a “PFAS test kit” expecting an instant answer. It is a mail-in lab service. Buy it knowing that, and compare it on laboratory price.
- Read your strip in consistent light, and compare against the chart at the stated time. Colour perception is the largest single error source, so anything you can do to standardise it helps more than buying a pricier strip.
- Treat any near-limit result as a reason to lab test, not as a result. Strips are least reliable near their own thresholds.
- Go straight to a certified lab if the result is for a sale, a loan, a dispute, or a decision about an infant’s water.
- Check what your state offers first. Several states test private wells free or at low cost, which can make the strip question moot.
Frequently asked questions
Are home water test kits accurate?
It depends entirely on the parameter. They are reasonable for pH, chlorine, hardness and nitrate, and unusable for lead and PFAS. A 2021 study of 16 at-home lead kits found 12 detected lead only at 5 to 20 mg/L, hundreds of times above the 15 ppb action level. There is no certification standard for consumer strips.
Can a test strip detect lead in water?
Not reliably. Most strips detect lead only at concentrations hundreds of times above the action level. The strips that do reach drinking-water levels detect dissolved lead only and miss particulate lead, which is the form that commonly comes from pipe scale and solder. A strip can read safe on dangerous water.
Is there a home test for PFAS?
No instant test exists. The limit is 4 parts per trillion for PFOA and PFOS, which requires laboratory mass spectrometry using EPA Methods 537.1 or 533. Every product sold as a PFAS home test kit is a sample collection kit that you mail to a laboratory.
Do nitrate test strips work?
Yes, and this is the clearest case where strips genuinely reach the regulatory level. A common strip has reading steps at 0, 1, 2, 5, 10, 20 and 50 mg/L as nitrogen, with a step at exactly the 10 mg/L limit. Check the units, since nitrate is reported both as nitrogen and as nitrate ion.
What does a TDS meter actually measure?
Electrical conductivity, converted to an estimated dissolved solids figure using an assumed factor. It cannot identify which ions are present, so it says nothing about lead, PFAS, bacteria or most organic compounds. TDS is a secondary standard at 500 mg/L, which the EPA does not enforce and treats as aesthetic.
Does a low TDS reading mean my water is safe?
No. Lead at the action level contributes essentially nothing to conductivity, PFAS at 4 parts per trillion contributes nothing, and bacteria are not ionic at all. A TDS meter is useful for tracking filter life, not for assessing safety.
Is the lead action level changing?
Yes. It is 15 ppb now and drops to 10 ppb on 1 November 2027 under the Lead and Copper Rule Improvements. Note also that lead’s health-based goal is zero, so the action level is a trigger for utility action rather than a safety threshold.
Can I use a home water test kit for a house sale or mortgage?
No. Lenders and property programmes generally require a result from a certified laboratory, often with the sample collected by a disinterested third party. Requirements vary by programme, so confirm with your lender before testing.
Are home bacteria tests any good?
They give a presence or absence answer, which is what the regulations require too. But they are not accepted for any official purpose, and compliance samples must reach a certified laboratory’s incubator within 30 hours, which a mailed kit cannot meet. Both the CDC and EPA direct well owners to certified laboratories.
Why do two people get different results from the same test strip?
Colour perception. In one evaluation, a colour-matching survey conducted with no strips at all reproduced 70 to 75 percent of the total variance in results. Individual users were self-consistent but differed from each other, and better instructions barely reduced the spread.
Is Tap Score a real lab?
Tap Score is the consumer brand of SimpleLab, which is a broker and network rather than a laboratory. It routes samples to independent accredited labs. Whether a result is accepted officially depends on which laboratory ran it and whether the receiving body accepts that lab’s certification in your state.
Should I test my well water at all if it is not required?
Yes. Private wells are federally unregulated and nobody will require it, which is precisely why it gets skipped. The CDC and EPA recommend annual testing for coliform bacteria, nitrate, total dissolved solids and pH. Several states offer this free or subsidised.
Related reading
- Well water testing cost by state (2026)
- NSF/ANSI 42 vs 53 vs 58 vs 401: what each certification covers
- What a water filter actually costs per gallon
- How to test water quality at home
Sources
- Kriss, R., Pieper, K.J., Parks, J., & Edwards, M.A. (2021). Challenges of Detecting Lead in Drinking Water Using at-Home Test Kits. Environmental Science & Technology, 55(3), 1964-1972.
- D’Andrea, L., & Kumpel, E. (2025). Evaluation of drinking water quality test kits for home use in the United States. Journal of Water and Health, 23(3), 350-363.
- Swinney, G.G., Mullins, S.A., Martin, J., Kinsey, J.B., & King, D.A. (2024). Evaluation of consumer water test strips. Journal of Undergraduate Chemistry Research, 23(4), 54-58, Taylor University. Cited as supporting evidence given the publication type.
- US EPA, Lead and Copper Rule and Lead and Copper Rule Improvements, for the 15 ppb action level and the November 2027 change to 10 ppb.
- US EPA, PFAS National Primary Drinking Water Regulation, for the 4.0 ppt limits and the status of the proposed partial rescission.
- US EPA, secondary drinking water standards, for the 500 mg/L TDS level and its non-enforcement.
- US EPA, Revised Total Coliform Rule, for certified laboratory and 30-hour incubation requirements.
- CDC, private well water testing guidance.
- Hach test strip specifications for nitrate (product 2745425) and arsenic (product 2800000), and Hach’s own description of strips as semi-quantitative pre-screenings.
- SimpleLab and Tap Score published descriptions of their laboratory network and accreditations. Vendor-stated; no independent audit found.
