Well Water Test Results: A Plain-English Guide to What They Mean

Water lab reports can feel overwhelming because they combine:

• unfamiliar names (like "total coliform" or "nitrite-N")
• units (mg/L, µg/L, pCi/L, ppt)
• abbreviations (MCL, MCLG, action level, reporting limit)

You don't have to become a chemist to use your results. You only need a clear process.

This guide gives you a step-by-step way to interpret your report without panic and without medical advice.

If you want deeper explanations of individual contaminants, use: Well water contaminants guide hub

Most well water test results fit into one of these categories.

A) Microbes (Bacteria Indicators)

These are usually reported as Present/Absent or Detected/Not Detected, not as a number.

Examples:

• total coliform
• E. coli
• fecal coliform (less common on homeowner panels)

This category is often the most urgent because it can point to a pathway for germs to enter the well.

B) Chemicals

These are usually reported as numbers.

Examples:

• nitrate
• arsenic
• lead (often at the tap)
• VOCs
• pesticides
• PFAS

Chemicals can be high without any taste or smell change, which is why testing matters.

C) Nuisance and Plumbing-Related Indicators

These usually affect taste, staining, scaling, and corrosion.

Examples:

• hardness
• iron and manganese
• pH
• total dissolved solids (TDS)

These are often not "emergencies," but they are very useful for diagnosing problems and choosing the right treatment if you want it.

You can ignore a lot of lab metadata at first. Focus on these parts.

Result

This is the measurement. For bacteria, it may be present/absent. For chemicals, it's usually a number.

Unit

Common units include:

• mg/L (milligrams per liter)
• µg/L (micrograms per liter)
• pCi/L (picocuries per liter, for radioactive contaminants)
• ppt or ng/L (parts per trillion or nanograms per liter, often used for PFAS)

Labs may define units once on the report. If not, ask.

Reporting Limit (or Detection Limit)

If a result is shown as "< 1.0" or "ND," it often means the lab did not detect the contaminant above its reporting limit.

That is usually good news, but it is still useful to know the reporting limit. For some contaminants, very low levels matter, so a lower reporting limit can be more informative.

Reference Value or Standard

Many reports show a reference value like an MCL (Maximum Contaminant Level) or action level.

Important context:

• Those standards are usually written for public water systems.
• Private wells are often not regulated the same way, but the standards are still widely used as a reference point.

If your report doesn't include reference values, you can ask the lab to help you interpret.

Before you interpret any number, confirm the sampling point.

Common sampling points:

• kitchen cold-water tap (most common)
• before treatment (raw well water)
• after treatment (what you drink)
• first draw sample (water that sat in plumbing)
• flushed sample (after running water briefly)

This matters most for metals like lead and for "first draw vs flushed sample" comparisons.

A result from "after reverse osmosis" can look great even if the raw well water isn't. That isn't necessarily a problem. It just answers a different question.

These longtail searches come up constantly:

• what does total coliform mean
• E. coli well water results
• nitrate levels in well water

Let's handle each in plain language.

What Does Total Coliform Mean?

What total coliform is (plain language)

Total coliform is a broad group of bacteria found in soil, plants, and surface water. Many total coliform bacteria aren't harmful on their own.

The reason labs test for total coliform is that it can act as an indicator. If coliform is getting into your well, it may mean your well has a pathway that could also allow harmful germs to enter.

EPA describes total coliform as a useful indicator for drinking water monitoring. (EPA)

What a positive total coliform result usually means

A "Present" or "Detected" result often means one of these:

• surface water is getting into the well (especially after rain)
• the well cap is damaged or not sealed properly
• the casing or seal has a defect
• the sample was accidentally contaminated during collection (this happens)

What to do when total coliform is positive (calm next steps)

Do not assume it is a disaster. Treat it as a "well vulnerability" signal.

1. Confirm sampling quality. Was the sample collected correctly? Was the bottle sterile?
2. Retest as recommended. Many people confirm with a repeat bacteria test.
3. Inspect the wellhead. Look for an obvious path in: loose cap, standing water, cracked casing area.
4. Address the cause. Fix drainage, replace a cap, repair the seal if needed.
5. Retest after corrections. Your goal is a clean follow-up result.

If you want deeper detail and troubleshooting steps, see: Total coliform bacteria in well water

E. coli Well Water Results: How to Interpret Them

What E. coli indicates

E. coli is used as an indicator organism. Its presence can suggest fecal contamination, which is why it's treated as more urgent than total coliform alone.

For public water systems, EPA's health goal (MCLG) for E. coli is zero. (EPA)

That doesn't mean you need to panic, but it does mean you should take action quickly and treat it seriously.

If E. coli is detected, what should you do right away?

The most practical immediate steps are:

• Do not drink the water until you have guidance and follow-up testing.
• Use bottled water or another safe source for:
  • drinking
  • cooking
  • brushing teeth
  • mixing baby formula
  • making ice

If you have no alternative source and you're dealing with a microbial concern, boiling can reduce risk from germs, but boiling doesn't remove chemical contaminants. If you're unsure what else may be in the water, ask your health department what they recommend for your situation.

Why "E. coli detected" doesn't always mean the well itself is permanently bad

E. coli can show up due to:

• flooding or heavy rain pushing contamination toward the wellhead
• a damaged well cap or unscreened vent
• well servicing that introduced bacteria
• septic system issues (depending on site conditions)
• sampling contamination (less common than with total coliform, but still possible)

The right next step is usually to treat it as a system problem to fix, then confirm by retesting.

If you want a full walkthrough, see: E. coli in well water

Nitrate Levels in Well Water: What the Numbers Mean

Why nitrate gets special attention

Nitrate is one of the most recommended annual chemical tests for private wells, and it matters most for households with infants.

Nitrate often comes from:

• fertilizers and agricultural runoff
• septic systems
• animal waste
• stormwater runoff
• natural sources in some settings

The key number people look for

EPA's maximum contaminant level (MCL) for nitrate in public drinking water is 10 mg/L. (EPA)

Important note: labs may report nitrate in different formats. Your report might show:

• "nitrate (as N)" or "nitrate-N"
• "nitrate" (as nitrate)

Those aren't the same number. If you're unsure how your lab is reporting nitrate, call them and ask. It's a normal question.

How to interpret nitrate results in a practical way

• If your nitrate is well below the reference level, it is generally reassuring.
• If nitrate is near the reference level, you should take it seriously and ask about:
  • confirmation testing
  • seasonal variation (some wells rise after heavy rain or spring runoff)
  • potential sources on or near the property
• If nitrate is above the reference level, prioritize exposure reduction for infants and ask about treatment and source control.

This is one area where "do nothing and wait" is rarely the best plan if results are high.

For more detail, see: Nitrates and nitrites in well water

Instead of staring at every line item, categorize results into three action levels.

Level 1: Needs Immediate Follow-Up (Usually Microbes)

Examples:

• E. coli detected
• other fecal indicators detected

Typical next steps:

• switch to a safe water source for drinking and cooking
• contact your lab or local health department
• investigate likely causes (wellhead, recent flooding, recent repairs)
• retest after corrective actions

Level 2: Needs a Plan (Chemicals Above Reference or Trending Upward)

Examples:

• nitrate elevated
• arsenic or lead above reference values shown on the report
• PFAS detected at levels of concern (if tested)

Typical next steps:

• confirm with a repeat test if recommended
• consider source investigation and targeted treatment
• retest on a schedule that matches the issue

Level 3: Mostly Quality-of-Life and Plumbing (Nuisance Indicators)

Examples:

• hardness high
• iron and manganese elevated
• pH low or high
• TDS elevated

Typical next steps:

• decide whether you want to treat for taste, staining, or appliance protection
• use results to choose the right equipment (if you choose treatment)
• keep a baseline record for future comparison

Most homeowners can do basic interpretation, but these situations are worth escalating:

• you have repeated bacteria positives
• you have nitrate near or above reference levels and infants are in the home
• results suggest a corrosion issue and you suspect lead at the tap
• you are buying or selling a home and need documentation and a plan quickly
• you're seeing multiple contaminants and don't know where to start

A state-certified lab can help interpret reports, and your local health department can often guide next steps.

To find options in your area: Find well water testing near me

If your report shows contamination, a calm, practical sequence usually works best:

1. Confirm the result if needed (especially if collection could have been flawed).
2. Reduce exposure when appropriate (especially for microbes and nitrate concerns).
3. Identify likely sources (well cap, drainage, flooding, septic issues, plumbing).
4. Fix the cause where possible, not just the symptom.
5. Retest to confirm the fix worked.
6. Keep a monitoring schedule that matches the problem.