What Do Your Water Test Results Mean? A Diagnostic Guide
What Do Your Water Test Results Mean? A Diagnostic Guide
Match each number on your lab report (or each symptom in your home) to what is actually going on, and get routed straight to the fix. Written by Aidan Walsh, 30+ years in residential water treatment.
TL;DR: Most water test results come down to nine patterns: hardness above 7 gpg (softener territory), iron above 0.3 mg/L (staining), pH below 6.5 (corrosion), hydrogen sulfide at any detectable level (rotten-egg smell), coliform bacteria (any positive is a fail), nitrate above 10 mg/L (urgent for infants), arsenic above 10 ppb, PFAS above the 2024 EPA limits, and TDS above 500 ppm. Each one maps to a specific treatment system, and every result below routes you to it. Have not tested yet? Start with the 53-contaminant certified lab well test ($199) or the city water version ($199). Already have results? Text or call Aidan at 800-460-5810 and he will read them for you, free.
How to read the report in 60 seconds
A certified lab report lists each contaminant, your measured level, and a comparison limit. Two kinds of limits matter. Health limits (EPA Maximum Contaminant Levels, or MCLs) are enforceable safety lines for things like nitrate, arsenic, lead, and bacteria. Aesthetic limits (Secondary MCLs) cover nuisance problems like iron staining, hardness scale, and sulfur odor; they will not hurt you, but they wreck fixtures, appliances, and laundry.
Read your report in this order: bacteria first (any coliform positive is a fail, full stop), then the health contaminants (nitrate, arsenic, lead, uranium, PFAS), then the nuisance panel (hardness, iron, manganese, pH, sulfur, TDS). If you want a deeper walkthrough of every line item and unit conversion, our full results interpretation guide goes number by number. This page is the fast version: find your flagged result below and follow the route.
Every result pattern, decoded and routed
These thresholds come from EPA primary and secondary drinking water standards. Where MAW's field experience says the practical trouble point differs from the regulatory line, the table says so.
| Result | Trouble level | What it means in your home | The fix |
|---|---|---|---|
| Hardness | Above 7 gpg | White scale on fixtures and glassware, dry skin, appliances dying early. Purely aesthetic, but the most expensive nuisance on this list over 10 years. | A properly sized water softener. Start with the softener guide or browse water softeners. |
| Iron | Above 0.3 mg/L | Orange-brown stains in toilets, tubs, and laundry; metallic taste. Above roughly 1 mg/L a softener alone cannot keep up. | An air-injection iron filter. Read the iron filter guide or browse iron filters. |
| pH | Below 6.5 | Acidic water slowly dissolves copper pipe: blue-green stains, pinhole leaks, elevated copper and lead at the tap. The damage is to your plumbing first, health second. | An acid neutralizer. Read the acid neutralizer guide or browse acid neutralizers. |
| Hydrogen sulfide | Any detectable | Rotten-egg smell, worse on hot water. No health limit exists because your nose finds it long before it is dangerous. | Air-injection sulfur filter or catalytic carbon. Read the sulfur guide or browse sulfur filters. |
| Coliform / E. coli | Any positive | Surface water or septic influence is reaching your well. E. coli positive means stop drinking untreated water now and use bottled or boiled water until it is fixed. | Shock chlorinate, retest, and install UV disinfection. Read the coliform removal guide or browse UV systems. |
| Nitrate | Above 10 mg/L | Serious for infants under 6 months and pregnant women (blue baby syndrome). Boiling makes it worse, not better. Often signals agricultural or septic influence. | Nitrate-selective filter or reverse osmosis. Read the nitrate guide or browse nitrate filters. |
| Arsenic | Above 10 ppb | Naturally occurring in bedrock in much of the country. No taste, no smell, no stain; only a lab test finds it. Long-term exposure is a known carcinogen. | Arsenic-specific media or RO. Read the arsenic guide or browse arsenic filters. |
| PFAS | Above 4 ppt (PFOA/PFOS) | The 2024 EPA rule set enforceable limits of 4 ppt for PFOA and PFOS. Private wells are not covered by the rule, so testing is on you. | Whole-house carbon or RO sized for PFAS. Read the PFAS guide or browse PFAS filters. |
| Manganese | Above 0.05 mg/L | Black specks and dark staining. EPA's health advisory for infants is 0.3 mg/L; the aesthetic limit is 0.05. | Same air-injection systems that handle iron. Read the manganese guide or browse manganese filters. |
| TDS | Above 500 ppm | Total dissolved solids. A high number alone does not say what is dissolved; it is a flag to look at the rest of the panel. Salty or mineral taste is common. | Reverse osmosis at the sink for drinking water. Read what TDS actually measures or browse RO systems. |
| Tannins | Any visible tint | Yellow to tea-colored water that does not clear on standing. Organic, from decaying vegetation; common near wetlands and shallow wells. | Tannin-selective resin. Read the tannins guide or browse tannin filters. |
| Lead | Above 10 ppb | Almost always from your own plumbing (solder, brass, old service lines), not the source water. Low pH makes it dramatically worse. | Fix the pH if acidic, then RO or lead-rated carbon for drinking water. Read the lead testing guide or browse lead filters. |
No lab report yet? Route by symptom
Symptoms narrow the suspect list, but they do not replace a test; two different problems can produce the same stain. Use these to know what to test for, then confirm with a certified lab panel like the 53-contaminant well test.
Not sure? Send Aidan your results. It is free.
This is how most of our customers actually figure out their water. Text a photo of your lab report (any lab's, not just ours) or call 800-460-5810 and Aidan Walsh will walk through it with you: what is fine, what needs treatment, and in what order. No commission, no pressure, and if your water is fine he will tell you that too.
Prefer email? Send your report through the contact page and he will reply with a written read.
Have not tested yet? Start here
Every kit below is analyzed by an independent certified laboratory and includes Aidan's free interpretation of the results.
- Private well: Well Water Test Kit, 53 contaminants ($199), or the Advanced Well Test, 113 contaminants ($329) if you have never tested or have a known problem history. Browse all well water test kits, including single-contaminant kits for confirming one suspect.
- City water: City Water Test Kit, 47 contaminants ($199). You can also look up your utility's public water quality data with the free city water report lookup on our whole-house filtration page.
Wondering whether lab testing is worth it over strips, or what it should cost? See lab tests vs DIY strips and what a well water test costs. For the full testing process (when, what, how to sample), start with the complete well water testing guide.
FAQ
What are the most important numbers on a water test?
Bacteria (total coliform and E. coli), nitrate, arsenic, and lead are the health-critical results; any of them out of range needs action, not monitoring. After those, pH, iron, manganese, hardness, and sulfide determine what equipment your house needs. TDS is a flag, not a diagnosis.
My test says everything is within limits. Do I need anything?
Possibly nothing, and we will say so. Aesthetic problems (staining, smell, scale) can still justify treatment even when every health number passes, because secondary limits are set for nuisance, not comfort. But if your report is clean and your home has no symptoms, keep the money and just retest annually for bacteria and nitrate.
Can I fix multiple problems with one system?
Sometimes. Air-injection filters handle iron, manganese, and sulfur together, and a softener handles hardness plus trace iron. But nobody should sell you one magic tank for bacteria plus arsenic plus hardness; those are different technologies in a specific order. Send Aidan the report and he will sequence it.
Why did my results change from last year?
Wells are dynamic. Rain, drought, nearby construction, agricultural cycles, and aquifer changes move iron, bacteria, and nitrate readings season to season. That is why EPA and state health departments recommend testing annually for bacteria and nitrate, not once ever.
Are DIY test strips good enough to act on?
Strips are fine for watching a known number move (like hardness after a softener install). They are not accurate enough to size equipment or to detect arsenic, lead, PFAS, or bacteria reliably. Buy equipment off a certified lab report, not a strip. Full comparison: lab vs strips.
Will Aidan really read a competitor lab's report for free?
Yes. Tap Score, WaterCheck, your county health department, a home inspector's report; the numbers are the numbers. Text a photo to 800-460-5810 or send it through the contact page. Interpretation is free either way.
What should I test for if I am on city water?
Your utility treats to federal standards at the plant, but lead and copper pick up in your own plumbing, and disinfection byproducts vary block to block. The city kit ($199) covers 47 contaminants including lead at parts-per-billion resolution. Start by reading your utility's annual report; the free lookup on our whole-house page pulls it by ZIP code.