How to read your well water test results

What is actually on the sheet

Most confusion about a water report is not about chemistry. It is about a document designed for a laboratory's obligations rather than for your decision, and the way through it is to know what each column is for.

Arizona's well owner guidance is the only source behind this page that describes the report as an object, and the description is short enough to hold in your head: most reports list the analytical detection limit, the MCL, and the result of your water analysis Source 4: University of Arizona Superfund Research Program, Well Owner's Guide4. Three columns, each answering a different question.

• Your result is what the method measured in your sample.
• The limit it is measured against is the published standard, and it is the column most likely to be missing or wrong, because a laboratory reporting to a homeowner is not always reporting against the same table you would choose.
• The detection limit is the floor of the instrument, and it is what makes a blank or a BDL mean something specific rather than nothing.

Two things follow, and both are the subject of the rest of this page. A result and a limit are comparable only in the same unit, which is not guaranteed and not always stated. And the limit column carries a fork, because the federal standards are two separate tables with two different purposes: that fork is covered in full in the testing guide, and this page assumes it and gets on with the sheet.

One limit, two numbers

Two rows on an ordinary well panel change meaning entirely depending on how the laboratory chose to state them, and the number on the page is identical either way. No contaminant reference can warn you, because the unit is a property of the report rather than of the contaminant.

Nitrate is reported two ways and only one of them matches the limit. The EPA writes the basis into the name of the row itself, which is the clearest signal you will get anywhere: the entry reads nitrate, measured as nitrogen, and its limit is 10 Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1. Texas well owner guidance supplies the conversion for the other basis, stating that ten mg/L of nitrate-nitrogen is equal to 44.3 mg/L nitrate Source 3: Texas Well Owner Network, Well Owner's Guide to Water Supply3.

Put those side by side and the trap is obvious. A report reading nitrate 30 is three times over the limit on the nitrogen basis and comfortably under it on the total basis. The number 30 is the same characters either way, and so is the row name, on a report that does not spell out the basis the way the federal table does.

This matters more than any other row because of who it is written for. The EPA's health note on nitrate is about infants below the age of six months, who can become seriously ill and, if untreated, may die, with shortness of breath and blue-baby syndrome named as symptoms Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1. That is a limit with a specific person behind it and a factor-of-four unit ambiguity on top of it. If there is an infant in the house and any doubt about the basis, the laboratory is a phone call away.

Arsenic is the same failure in a smaller unit. Its federal limit is 0.010 mg/L Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1. The Arizona guidance states the identical limit as 10 parts per billion, and then, a few pages later, writes it a third way as arsenic above 10 ug/L Source 4: University of Arizona Superfund Research Program, Well Owner's Guide4.

One authority prints both, in one document. All three are the same concentration, and a report reading arsenic 8 is either comfortably under the limit or eight hundred times over it depending on which scale it is on.

One rule resolves most of these, stated in the federal table's own notes: figures are in milligrams per liter unless otherwise noted, and milligrams per liter are equivalent to parts per million Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1. Milligrams per liter and parts per million are interchangeable, micrograms per liter and parts per billion are interchangeable, and the two families are a thousand apart. A number without its unit is not a result.

The bacteria row has no number to compare

The row most people turn to first is the one where the yardstick does not exist for you. That is worth understanding rather than working around, because the alternative is comparing your result to a rule that was never about your well.

Total coliform appears on the federal primary table with a goal of zero and a limit of 5.0 percent Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1. That is not a concentration. The footnote states what it counts: no more than 5.0 percent of samples total coliform-positive in a month, and for water systems collecting fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month Source 1: United States Environmental Protection Agency, National Primary Drinking Water Regulations1.

Read that as a homeowner and the problem is structural rather than arithmetic. The standard is a rule about a sampling program run by a water system over a month. A household well has no sampling program and no month: it has one bottle, collected once, at one tap.

No private-well limit exists for that result, and there is no honest way to convert a percentage-of-samples rule into a threshold for a single sample. Present or absent is the only reading the sheet supports.

What presence means is a separate question, and NGWA answers it without a number. Well water is typically sampled first for total coliform bacteria, which are not necessarily harmful, and a positive test indicates that the conditions exist in the well to support other types of bacteria, including pathogenic bacteria Source 5: National Ground Water Association, Well Owner's Guide 20215. Its instruction from there is to consult your drinking water testing laboratory about doing further testing for pathogenic bacteria Source 5: National Ground Water Association, Well Owner's Guide 20215.

So a positive reads as a sequence rather than a severity. Stop drinking it while you confirm it. Retest at a certified laboratory, because a single positive can be a sampling error at the tap.

If it confirms, the well needs disinfecting, and the shock chlorination guide carries that procedure with the chemical handling warnings it requires. This page names the step and not the method. Again, your county health department has the final word.

Row by row, and the one class of treatment that answers each

What follows is a router rather than a shopping list. Each row names its yardstick, what exceeding it produces, and the single class of treatment the sources put it in. A class is not a product, and nothing here selects an appliance.

• Total coliform or E. coli, present. No comparable limit, as above. Confirm, then disinfect the well. Routed to the shock chlorination guide, and to the laboratory for the pathogenic follow-up.
• Nitrate, over 10 mg/L as nitrate-nitrogen. A health limit with infants as the named risk. NGWA puts nitrate treatment in two classes: reverse osmosis, typically at a single tap where water is used for drinking and cooking, or ion exchange with a resin selected for nitrate Source 5: National Ground Water Association, Well Owner's Guide 20215. The trap here is that a water softener is also an ion exchange unit and is not this one. The softener guide resolves that apparent contradiction in full, and its answer is that a unit configured for nitrate is a different application with a different resin than the one you got when you asked for softer water.
• Arsenic, over 0.010 mg/L. A health limit. NGWA names reverse osmosis, usually accompanied by granular activated carbon as the water enters and exits the membrane, as the treatment class Source 5: National Ground Water Association, Well Owner's Guide 20215. Point-of-use rather than whole-house is the usual shape, for the same reason as nitrate: the water you drink is a small fraction of the water you use.
• Iron, over 0.3 mg/L. Manganese, over 0.05 mg/L. Both are secondary standards, so neither is a health number. The EPA states the effect beside each: rusty color, sediment, metallic taste and reddish or orange staining for iron, and black to brown color, black staining and a bitter metallic taste for manganese Source 2: United States Environmental Protection Agency, Secondary Drinking Water Standards2. Which treatment applies depends on the form the iron is in rather than the amount alone, and the iron guide is the page that sorts that out.
• Hardness, at any number. There is no row for it on either federal table, and Texas states the reason plainly: there are no primary or secondary standards for water hardness Source 3: Texas Well Owner Network, Well Owner's Guide to Water Supply3. A hardness result is therefore never an exceedance of anything. It is a scale and soap number, and the softener guide covers what it means and how the three scales it is reported on relate.
• pH outside 6.5 to 8.5. Total dissolved solids over 500 mg/L. Sulfate or chloride over 250 mg/L. Secondary standards again, and the EPA lists the effects: bitter metallic taste and corrosion at low pH, a slippery feel and deposits at high pH, salty taste for sulfate and chloride, and hardness, deposits, colored water and staining for total dissolved solids Source 2: United States Environmental Protection Agency, Secondary Drinking Water Standards2. These are the rows a treatment installer cares about most and a health decision cares about least, because they decide whether equipment fouls.
• A rotten-egg smell with no row on the report. Odor carries a secondary standard of 3 threshold odor number, which the EPA describes as a rotten-egg, musty or chemical smell Source 2: United States Environmental Protection Agency, Secondary Drinking Water Standards2. Most panels do not test for it, so its absence from your sheet is not its absence from your water.
• Radionuclides, uranium, radon, or anything on a local concern list. Named as classes and routed outward on purpose. NGWA gives granular activated carbon and aeration for radon, and reverse osmosis, ion exchange or distillation for uranium Source 5: National Ground Water Association, Well Owner's Guide 20215, and every one of those carries handling and disposal conditions this page does not cover. Your county or state health department knows which of these are a real problem where you live, and no national list can tell you.

Requirements vary by county. Your county health department has the final word on permits, inspections, and what is allowed on your property.

Not detected is a number, and your panel has an edge

Two blanks on a report read as good news. Only one of them is.

A non-detect is bounded by the method, not by zero. Arizona states it exactly: BDL means that if a constituent was present in your sample, it was below the laboratory analytical detection limit Source 4: University of Arizona Superfund Research Program, Well Owner's Guide4. The useful version of that result is therefore less than the detection limit, and that limit is printed on the same row.

Where a standard sits far above the floor of the method, the distinction is academic. Where it sits near it, compare the two before you file the report.

A row that is not on the report was not tested. A panel measures what was ordered, and everything else is absent from the page rather than from the water. This is also the honest limit of a strip kit, and both extension sources say so in nearly the same words.

Arizona: some kits provide only a negative or positive result, which is of limited use since you still will not know if the concentration is above the MCL Source 4: University of Arizona Superfund Research Program, Well Owner's Guide4. Texas: a negative or positive result is of limited use if the MCL is more than zero Source 3: Texas Well Owner Network, Well Owner's Guide to Water Supply3.

What the sheet says depends on how the lab wrote it

Reading the report is yours. Acting on a row that carries a health limit is where this page stops and other people start.

If you are holding a report today, the order that respects every source here is short.

• Match every number to its unit first, because a wrong unit makes every later step wrong.
• Split the rows into health and appearance, and read the health rows first.
• Treat any bacteria presence as real until a retest says otherwise.
• Then ask your county what is a local problem where you live, because that part is binding and the rest of this page is not.

How we verify explains why nothing here carries a price: there is no dated pricing track behind testing or interpretation, and a national figure would be wrong somewhere the day it went up.