Reading a well water test

Best for

Well owners holding a lab report who want to know which numbers matter, which are fine, and what to do next.

Wrong fit

Anyone holding only a salesperson's in-home test or a strip reading. Get a certified lab test first, then use this guide.

Tradeoff

EPA limits are written for public water systems. They're the right benchmark for a private well, but no agency enforces them on your well.

How a report is laid out

Most lab reports have the same columns. Penn State Extension walks through them in its guide to interpreting test reports:

• Sample information. Your name, the lab ID, when and where the sample was collected. Check the collection date and location. A sample from the pressure tank tells you about raw well water; a kitchen tap sample shows what you drink after any treatment.
• Analysis. What was tested.
• Units. mg/L, µg/L, MPN/100 mL and so on.
• Result. Your number.
• Standard. The limit your result is compared against, and whether it is health-based or aesthetic.
• Method. The EPA or standard method the lab used. Certified labs have to use approved methods.

Some reports also flag results that exceed a standard and list a contact for questions.

Units and symbols

Penn State explains that labs don’t report zero. When nothing is found, the result is shown as “less than” the detection level. A “greater than” sign on bacteria means more colonies than the method can count.

Watch the unit before you compare. Arsenic at “0.008” in mg/L is 8 µg/L, under the 10 µg/L limit. The same “8” in mg/L would be a thousand times higher. Nitrate limits are written “as nitrogen.” Check that your lab reports it the same way.

Health-based results: act on these first

These limits come from EPA’s National Primary Drinking Water Regulations for public water systems. They’re the standard benchmark for private wells too.

EPA says infants under six months who drink water with nitrate above 10 mg/L could become seriously ill. For manganese, EPA’s health advisory document flags concern for infants, and the Minnesota Department of Health uses a guidance value of 100 µg/L for infants who drink tap water or formula made with it, and 300 µg/L for everyone over one year old.

For any result in this table, call your state health department. They can tell you how urgent it is and whether to retest. See bacteria, nitrate, arsenic and manganese.

Aesthetic results: stains, taste and scale

These are EPA’s secondary standards. EPA calls them guidelines and does not enforce them. They mark where cosmetic and aesthetic problems usually start.

Iron below 0.3 mg/L may need nothing at all. More on iron in well water.

Results with no EPA number

Some useful results don’t have a federal limit:

• Hardness. Penn State classes water from soft (below 1 gpg [17 mg/L]) to very hard (above 10.5 gpg [180 mg/L]), with 7.0 to 10.5 gpg [120 to 180 mg/L] counted as hard. See hard well water.
• Hydrogen sulfide. No drinking water standard, because the smell makes water undrinkable well before it is harmful. Penn State says most people smell it well below 0.5 mg/L. The sample must be stabilized or tested on site.
• Corrosivity index (LSI). Penn State says negative values indicate corrosive water. Pair it with a first-draw lead and copper test.
• Sodium. Useful if anyone in the home is on a low-sodium diet, especially if you soften.

A worked example

Here is an illustrative report for a well with common nuisance problems. The numbers are an example, not real data.

What this report says, in order:

1. No health emergency. Bacteria, nitrate and arsenic are fine.
2. Low pH comes first in treatment. At 6.3 it’s below the secondary range and below what some iron filters require. Penn State notes negative corrosivity and low pH go with corroded plumbing, so test first-draw lead and copper.
3. Iron and manganese next. Both are above the staining levels.
4. Hardness last. A softener goes after the iron filter, and a calcite neutralizer would add a bit more hardness.

The treatment order would be neutralizer, then iron and manganese filter, then softener.

Red flags on a report

• No lab name or certification. Penn State stresses that state-accredited labs are vital for accurate, unbiased results.
• No units, or units you can’t match to a limit.
• No method column. Penn State notes methods are required as part of state lab accreditation.
• A report from the company selling you equipment with no independent lab behind it.
• A bacteria result from a sample that sat for days before reaching the lab.

Turning results into a plan

1. Health results over a limit: switch drinking water now, then retest to confirm and call your health department.
2. Bacteria only, no E. coli, first time: shock chlorinate and retest before buying equipment. See how to test well water for sampling steps.
3. Several aesthetic problems: treatment order matters. Sediment, then pH, then iron, manganese and sulfur, then softening, then UV.
4. Missing results: if your report lacks iron, manganese, hardness or pH and you’re planning treatment, add them before you buy anything.

Enter your numbers at /test-results/ to get a treatment plan built from them.