Well water test results explained: hardness, iron, manganese, sulfur and pH

Five numbers in your well water test results decide which softening or filtering equipment you need: hardness, iron, manganese, hydrogen sulfide and pH. Above about 3.5 grains per gallon (60 mg/L) of hardness, most households start to notice scale, and a softener is worth considering. Iron above 0.3 mg/L or manganese above 0.05 mg/L means staining, and the amount decides between a softener and an iron filter. Hydrogen sulfide is the rotten-egg smell, and pH sets limits on which equipment will work.

This guide covers only those nuisance numbers. Everything else on a lab report, such as bacteria, nitrate, arsenic or lead, needs a certified lab to interpret it, and we explain where to go for those at the end.

How to read the units on your well water test results

Most of the confusion on a water test is units. Three rules cover nearly every report:

• mg/L and ppm are the same number. 0.5 mg/L of iron is 0.5 ppm of iron.
• Hardness has its own unit, grains per gallon (gpg). Softener manuals and calculators use gpg.
• To convert hardness, divide mg/L “as CaCO3” by 17.1. A report showing 257 mg/L as calcium carbonate is 15 gpg. The 17.1 comes from the size of a grain (64.8 mg) and a US gallon (3.785 L), as the grain per gallon definition shows. Penn State rounds it to 17.

If your report lists calcium and magnesium separately instead of total hardness, ask the lab for total hardness as CaCO3. It saves a conversion step that is easy to get wrong.

Well water test results chart

This is the table to keep next to your report. The ranges come from Penn State Extension, EPA’s secondary standards and manufacturers’ published limits.

Plug your own numbers into the treatment matcher in our iron filter vs water softener guide. It applies these rules and shows a note for each one your water trips.

Hardness

Penn State Extension’s water softening guide classifies hardness like this:

Hardness is scale: white crust on fixtures, spots on glass, and buildup in water heaters. Under 1 gpg, you don’t need a softener. From moderately hard up, most households notice scale. Once you know your gpg, the softener size calculator turns it into a resin volume and a salt setting.

Reading the iron result (dissolved or red, total or ferrous)

EPA’s secondary standard for iron is 0.3 mg/L. EPA calls secondary standards non-mandatory guidelines for aesthetic effects such as taste, color and odor, and lists iron’s effects as rusty color, sediment, a metallic taste and reddish or orange staining. So a number above 0.3 on your report is a staining problem, not a health verdict.

What matters for equipment is the form of the iron:

• Dissolved (ferrous, clear-water) iron is invisible when the water leaves the tap and turns orange as it meets air. A softener can remove it by ion exchange.
• Oxidized (ferric, red) iron is already particles. The water looks orange or cloudy from the start. Penn State says this iron clogs softener resin, so it has to be filtered out first.

Most labs report total iron. For a simple check, fill a clear glass straight from the tap. If it comes out clear and turns orange or drops sediment after a few hours, most of your iron is dissolved. If it is orange right away, you have oxidized iron. You can also ask the lab for dissolved (ferrous) iron as a separate line.

Penn State’s iron and manganese guide recommends a softener for iron only when dissolved iron is under 5 mg/L, hardness is 3 to 20 gpg and pH is above 6.7. It lists an oxidizing filter for iron plus manganese of 3 to 10 mg/L, and oxidation followed by filtration above 10.

Manganese

EPA’s secondary standard for manganese is 0.05 mg/L, much lower than for iron. Its effects are black to brown color, black staining and a bitter metallic taste. Black specks in the toilet tank or dark stains in the laundry usually mean manganese.

Softeners exchange some manganese along with iron, but no softener manual we read gives a factor for sizing it. Our size calculator leaves manganese out of the math and shows a warning instead. With manganese on your report, look at iron filters and compare their manganese limits: SpringWell’s WS filter lists 1 ppm and SoftPro’s Iron Master 7 ppm. Our roundup of the best iron filters for well water sets five filters’ iron, manganese and sulfur limits side by side. Penn State adds that polyphosphate treatment is generally ineffective for manganese.

Hydrogen sulfide and pH

Hydrogen sulfide (H2S) is the rotten-egg smell. It escapes from water quickly, so Penn State’s hydrogen sulfide guide says the test must be done at the home, or the sample chemically stabilized before it goes to a lab. A value from an unstabilized bottle will read low. Penn State’s treatment ranges are activated carbon under 1 mg/L, aeration up to about 2 mg/L, an oxidizing filter up to 2 to 3 mg/L and continuous chlorination above 6 mg/L.

If the smell only comes from the hot tap, the water heater’s magnesium anode is a common cause, and Penn State suggests swapping it for an aluminum anode. Our guide to the sulfur smell in well water covers the other causes and the treatment for each.

pH matters here as an equipment limit. EPA’s secondary range is 6.5 to 8.5; low pH brings a metallic taste and corrosion, high pH a slippery feel and deposits. Equipment has its own ranges:

• Penn State recommends softening for iron only above pH 6.7
• WaterBoss 900 softener: minimum pH 7, per its manual
• SpringWell SS softener and WS iron filter: pH 6.5 to 10
• Salt-free conditioners: SpringWell FutureSoft 7.0 to 9.5, Aquasana SimplySoft below 8.3

If your pH is under 7, confirm the range of any product before you buy it.

What to ask the lab for before buying equipment

A basic bacteria-and-nitrate test won’t size a softener or choose a filter. Before you shop, make sure your results include:

1. Total hardness, as CaCO3 in mg/L or in gpg
2. Total iron, and dissolved (ferrous) iron if the lab offers it
3. Manganese
4. pH
5. Hydrogen sulfide, tested on site or from a stabilized sample
6. Your well’s flow rate, which no lab measures. Time how long a 5 gallon bucket takes to fill at a tap near the pressure tank with the pump running, then divide 5 by the minutes.

The flow rate matters because backwashing iron filters need a minimum flow. SoftPro’s Iron Master, for example, needs 5, 7 or 10 gpm depending on size. With all six numbers you can use the matcher, then go straight to our picks of the best water softeners for well water. If you were leaning toward a salt-free unit, read whether salt-free softeners work first: they need iron and manganese removed before they can work at all.

Health-related results go to a certified lab

We don’t interpret results for bacteria, nitrate, arsenic, lead or any other health-related contaminant, and this site does not cover treatment for them. For health-related contaminants, test with a certified lab and choose equipment certified to the matching NSF/ANSI standard.

NSF explains which standard covers which kind of system on its water treatment standards page. The ones you are most likely to see:

• NSF/ANSI 44: cation exchange water softeners (NSF page)
• NSF/ANSI 42 and 53: filtration systems, with 53 covering health-related contaminant reduction (NSF page)
• NSF/ANSI 58: point-of-use reverse osmosis systems (NSF page)
• NSF/ANSI 55: ultraviolet systems, and NSF/ANSI 62: distillation systems (both on the standards page above)

NSF notes that manufacturers choose which contaminants they certify for, so check the product for both the standard number and a claim for the specific contaminant on your report. More guides on iron, sulfur and well treatment are in our well water section.