How to Read a Well Water Test in Idaho
A well water test report is a page of chemical names, units, and "ND" or "<0.01" entries that most people glance at once and file away. That's a shame, because the numbers on it decide whether your water is safe to drink and what kind of treatment — if any — actually makes sense. I'm a water treatment installer based in Moscow, and I read these reports for well owners around Latah County every week. This article walks through what's on a typical report, which numbers matter on Palouse wells, and what each one means for your house.
If you want the bigger picture of why wells here run high in iron, manganese, and hardness, that's covered in the Palouse well water guide. This page is about the report itself.
Who is responsible for testing a private well in Idaho
You are. Private domestic wells aren't regulated under the federal Safe Drinking Water Act, and Idaho DEQ notes there are no statewide water quality regulations for them — testing is recommended, not required. The Idaho Department of Health and Welfare recommends that private well owners test for bacteria and nitrate every year, test nitrate more often if a pregnant woman or infant uses the water, and test for arsenic, uranium, and fluoride once every three to five years.
The limits you'll see printed on a lab report are the EPA's public water system standards. They don't legally apply to your well, but they're the right yardstick. There are two kinds: MCLs (maximum contaminant levels), which are health-based, and secondary standards, which are non-enforceable guidelines for taste, odor, staining, and scale.
Basic panel vs. full panel
Labs name and bundle their packages differently, so always look at the list of analytes, not the package name. In general:
- A basic or "safety" panel usually covers total coliform and E. coli bacteria and nitrate (often nitrite too). Some add lead. This is roughly what a mortgage lender asks for.
- A full or "comprehensive" panel adds the chemistry: hardness, iron, manganese, pH, total dissolved solids, sulfate, chloride, and often arsenic, fluoride, copper, and uranium.
The basic panel answers "is it safe to drink right now." The full panel answers "what is this water going to do to my plumbing, fixtures, and laundry, and what will fix it." For a treatment design, you need both.
The numbers that matter on Palouse wells
Here's how I read the parameters that come up most on wells around Moscow, Troy, Genesee, Deary, and the Highway 6 corridor. Standards are the EPA's; "secondary" means an aesthetic guideline, not a health limit.
| Parameter (units) | EPA standard | What the number means for treatment |
|---|---|---|
| Total coliform / E. coli (present / absent) | E. coli has a health-based MCL; the goal for both is zero | Any positive matters. E. coli points to human or animal waste — don't drink it untreated. See what to do after a positive coliform test. |
| Nitrate (mg/L as N) | MCL 10 mg/L; nitrite MCL 1 mg/L | A health limit, and infants are most at risk. Elevated nitrate often points to fertilizer, septic, or livestock influence. Reverse osmosis at the drinking tap is a common answer. |
| Hardness (mg/L as CaCO3, or gpg) | No EPA standard | 7+ grains per gallon is hard. Softener territory — and hardness changes how other equipment performs. |
| Iron (mg/L) | Secondary 0.3 mg/L | Staining starts around 0.3. The form of the iron decides the equipment (more below). |
| Manganese (mg/L) | Secondary 0.05 mg/L; EPA lifetime health advisory 0.3 mg/L | Black staining at very low levels. Above 0.3 it's a health question, not just a cosmetic one. Harder to remove than iron. |
| pH (standard units) | Secondary 6.5–8.5 | Low pH is corrosive to copper and fixtures. Below ~6.8 or above ~8, oxidation-based iron and manganese removal gets unreliable. |
| Total dissolved solids (mg/L) | Secondary 500 mg/L | A catch-all for everything dissolved. High TDS with high hardness is normal; high TDS with low hardness means something else is in there worth identifying. |
| Sulfate (mg/L) | Secondary 250 mg/L | Salty or bitter taste above the guideline. Different from hydrogen sulfide, the rotten-egg smell, which is a gas and is best checked at the tap. |
| Tannins (mg/L) | No EPA standard | Tea-colored water that doesn't settle. Tannins can bind iron and defeat standard iron filters and softeners. |
| Arsenic (mg/L or µg/L) | MCL 0.010 mg/L (10 µg/L) | Idaho's well-known arsenic areas are in the southern part of the state, but it's naturally occurring and on the state's every-three-to-five-years list. Worth a baseline result on any well. |
One reading tip: "ND" or "<" followed by a number means the lab didn't detect it above their reporting limit. That's a good result. Make sure the reporting limit is below the standard you care about — a manganese result of "<0.1" can't tell you whether you're over the 0.05 staining threshold.
Converting mg/L to grains per gallon
Lab reports usually give hardness in mg/L (sometimes written "mg/L as CaCO3" or ppm). Softeners are sized in grains per gallon. The conversion is simple: divide mg/L by 17.1.
- 120 mg/L ÷ 17.1 ≈ 7 gpg — the start of "hard" on the Water Quality Association's scale
- 180 mg/L ÷ 17.1 ≈ 10.5 gpg — the start of "very hard"
- 250 mg/L ÷ 17.1 ≈ 14.6 gpg
If your well also has dissolved iron and manganese, a softener has to handle those too, so I size for the combined load rather than the hardness number alone. That's one reason a softener sized off a hardness strip alone tends to run out of capacity on Palouse water. More on that on the water softener page.
Why the form of iron and the pH matter more than the iron number
Two wells can both show 2.0 mg/L of iron and need completely different equipment. What decides it:
- Dissolved (ferrous, "clear-water") iron comes out of the tap clear and turns orange after it sits. A properly configured softener can often remove moderate amounts of it along with hardness and manganese.
- Oxidized (ferric, "red-water") iron is already particles when it leaves the tap. It fouls softener resin and needs filtration instead.
- Organic or tannin-bound iron resists oxidation and slips through many standard iron filters. This is a common reason a previous system "never worked."
- Iron bacteria leave a reddish slime in toilet tanks and can make an iron problem much worse. They aren't a health threat, but they change the design.
Most lab reports give only "total iron," which lumps these together. That's why I look at the water fresh from the tap, check for tannins, and read the iron number against the pH. Oxidation-based filters depend on pH, and manganese in particular oxidizes slowly at the pH many Palouse wells have. A report with iron and no pH isn't enough to design anything. The iron and manganese removal page covers the equipment side.
What the lender or realtor test usually skips
If you bought your place with a mortgage, you may have a well test in your closing paperwork. Lender-driven tests generally focus on bacteria and nitrate/nitrite, sometimes lead. That's a reasonable safety check, but it usually says nothing about hardness, iron, manganese, pH, tannins, TDS, or arsenic — the numbers that decide whether your fixtures stain and what treatment you need. A passing lender test and orange toilets are not a contradiction. If you're in the middle of a purchase, see buying a home with a well in Latah County.
Where to get lab testing in Idaho
For bacteria, nitrate, arsenic, and anything a lender or doctor will rely on, use a certified lab. The Idaho Bureau of Laboratories (part of the Department of Health and Welfare) certifies labs for drinking water testing and publishes the list of certified labs, and Idaho DEQ's private well pages link to it. Public Health – Idaho North Central District, which serves Latah County, is another good place to ask about testing options and sample drop-off.
How my on-site test fits in
When I come out, I test hardness, iron, manganese, pH, and more at your tap, in front of you. That gives fresh, same-visit numbers for the parameters that drive equipment design — including things lab reports tend to blur, like whether the iron is dissolved or already oxidized, and whether tannins are in the mix. It's not a certified lab result, and it's not a substitute for one where safety is concerned. If bacteria, nitrate, or arsenic haven't been checked recently, I'll tell you to get a certified lab test, and I design around both sets of numbers. If you already have a lab report, send it along and I'll read it with you. After an install, I test the treated water so you can see the before and after.
More on how that visit works is on the water testing page. Common questions are in the FAQ, and if you're not sure where your water stands yet, take the 2-minute water quiz.
Have a well test you can't make sense of?
Send it over or have me test on-site. I'll walk you through what the numbers mean and what your water actually needs — even if the answer is "nothing."
Text Trent Call (208) 883-4444