How to Read Your Well Water Test Results (Without a Chemistry Degree)

You got your well water test results back. Now you're staring at a table full of numbers, abbreviations, and units you've never seen before. What does it all mean?

Here's a plain-English guide.

The Basic Structure

Most lab reports follow the same format. For each contaminant tested, you'll see:

• Parameter — What was tested (e.g., "Total coliform bacteria," "nitrates as N," "arsenic")
• Result — What was found in your sample, in specific units
• Units — How the result is measured (mg/L, µg/L, CFU/100mL, etc.)
• MCL — Maximum Contaminant Level (the EPA's legal limit for public water)
• Status — Often "Pass/Fail," "Detected/Not Detected," or flagged with an asterisk

Understanding the Units

The units can be confusing. Here's a quick reference:

| Unit | Meaning | Used for | |------|---------|----------| | mg/L | Milligrams per liter (= ppm, parts per million) | Nitrates, iron and manganese, hardness, most common | | µg/L | Micrograms per liter (= ppb, parts per billion) | Arsenic, lead, heavy metals | | ng/L | Nanograms per liter (= ppt, parts per trillion) | PFAS | | CFU/100mL | Colony forming units per 100 mL | Bacteria | | pCi/L | Picocuries per liter | radon |

What the MCL Means (and Doesn't Mean)

The MCL is the EPA's enforceable limit for public water systems. It's set based on a balance between health risk and what's technically and economically achievable to treat.

Important caveats:

• The MCL is not a "safe" line — it's a regulatory threshold. Some health advocates recommend acting at levels below the MCL for certain contaminants (arsenic, PFAS, lead).
• Private wells aren't legally required to meet MCLs — the rules apply to public water systems. But MCLs are still your best reference point.
• "Not Detected" doesn't mean zero — it means below the lab's detection limit, which is a very small amount. This is fine for most contaminants.

Common Results Explained

Total Coliform: Absent / Present Absent = good. Present = action needed. Your lab report should also test specifically for E. coli if total coliform is present. Any detection of E. coli is a serious finding requiring immediate action (don't drink the water, call your health department).

Nitrate: X mg/L (MCL = 10 mg/L) Below 10 mg/L is acceptable. Above is a concern, especially for infants. Between 5–10 mg/L is worth watching.

pH: X (ideal range 6.5–8.5) Below 6.5 is acidic — can corrode pipes and leach metals. Above 8.5 is basic — usually not a health concern but affects taste and can cause scale buildup.

Arsenic: X µg/L (MCL = 10 µg/L) Some researchers recommend treatment at levels above 3–5 µg/L, below the EPA MCL. Even "non-detect" for arsenic is reassuring.

Lead: X µg/L (action level = 15 µg/L) Lead in well water usually comes from plumbing, not the aquifer. The EPA's action level is 15 µg/L, but the agency says there is no safe level of lead exposure. Any detection warrants investigation of your plumbing.

PFAS: X ng/L (EPA limits: 4 ng/L for PFOA/PFOS) The EPA's 2024 rule sets limits at 4 parts per trillion — incredibly small amounts. If your report shows any PFAS above these limits, consult your health department.

Iron/Manganese: X mg/L Iron MCL is 0.3 mg/L; manganese is 0.05 mg/L. These are secondary standards (aesthetic, not health-based) — but elevated levels cause staining, taste issues, and can clog pipes.

What to Do If Something is Flagged

1. Don't panic — one result above an MCL doesn't mean your water is immediately dangerous (except bacteria — act immediately on that)
2. Call your county health department — most offer free consultation on well water results
3. Get a second test — if a result surprises you, confirm it with a re-test before spending money on treatment
4. Talk to a water treatment specialist — treatment options exist for almost every contaminant

Keep Your Results

Store your test results somewhere you won't lose them. They're your baseline. When you re-test next year, you'll want to compare. They're also useful documentation if you ever sell the property.

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