Softener sizing for well water

On a private well, test before you size: you need hardness, iron, manganese and pH, not just hardness. The one sizing adjustment the Morton, Whirlpool, Rheem and WaterBoss manuals print is for clear-water iron: add 5 grains per gallon to your hardness for each 1 ppm of iron. The iron must also be within the limit of the model you choose.

Test first

No agency monitors a private well for you (CDC). Private wells are not regulated by the federal government or by most states, and the owner is responsible for the water (EPA). CDC says to test at least once a year for total coliform bacteria, nitrates, total dissolved solids and pH, using a state-certified laboratory (CDC). Our well water testing guide covers that yearly test.

For a softener, add:

• Hardness, in grains per gallon or mg/L.
• Iron, and which kind. Minnesota's health department also suggests testing pH, alkalinity and iron bacteria when you test for iron (MDH).
• Manganese. The only way to know the level is a test from an accredited laboratory (MDH).
• pH. The WaterBoss 900 needs a pH of 7 or above (WaterBoss manual).

Softeners are not disinfection. The Morton manual says not to use one on water that is microbiologically unsafe or of unknown quality without disinfection (Morton manual).

The iron adjustment

The Morton, Whirlpool and Rheem manuals all say: add 5 to the hardness number for each 1 ppm of iron. Their example is 20 gpg water with 2 ppm iron, entered as 30 (Whirlpool WHES40 manual). WaterBoss gives the same rule for ferrous iron (WaterBoss manual).

So the formula becomes (hardness + 5 × iron in ppm) × people × gallons per person per day × days between regenerations. Example: 12 gpg and 1 ppm iron, 3 people, 82 gallons each, 7 days. Without iron that is 20,664 grains; with it, 17 × 3 × 82 × 7 = 29,274 grains. Enter 17 as the hardness in the softener size calculator.

None of the seven softener manuals and data sheets we read gives an adjustment for manganese, so we do not give one; ask the maker. WaterBoss also says not to use potassium chloride when the water contains iron or manganese (WaterBoss manual).

Iron limits by model

These are the makers' figures. Minnesota's health department says manufacturers report some softeners can remove up to 10 mg/L of iron, but 2 to 5 mg/L is a more common limit (MDH). The Morton, Whirlpool and Rheem manuals add that Wisconsin requires extra treatment above 5 ppm of clear-water iron (Rheem manual).

Only clear-water iron

A softener handles ferrous, or clear-water, iron: the water comes out clear and turns red or brown after standing (MDH). The Morton manual says its softeners will not remove ferric (red-water), bacterial or colloidal iron; ferric iron is generally removed by filtration (Morton manual). MDH adds that iron plugs a softener and has to be backwashed out, and that with organic iron and tannins, softeners and iron filters may not work well (MDH).

Upkeep the manuals ask for with iron: a resin bed cleaner every six months (WaterBoss manual), and, optionally, a forced regeneration every few days to keep the resin clean (Whirlpool WHES40 manual).

Iron above a model's limit, or iron that is not the clear-water kind, calls for treatment ahead of the softener. WaterBoss says ferric iron should be filtered out before the water reaches the softener (WaterBoss manual). Two well filters in our list, the SpringWell WS1 and the Home Master HMF3SdgFeC, make iron and manganese claims: Brand claim, no certification cited. Home Master lists its limits as iron below 3 ppm and manganese below 1 ppm (Home Master). Salt-free conditioners are no fix here: Watts wants iron below 0.3 ppm and manganese below 0.05 ppm (Watts specification); see salt vs salt-free softeners.

What the numbers mean

EPA's secondary standards are 0.3 mg/L for iron and 0.05 mg/L for manganese. They cover staining, color and taste, and they are not federally enforceable (EPA). MDH says iron in water does not usually present a health risk (MDH). For manganese, MDH's guidance values are 100 µg/L for infants who drink tap water or formula made with it, and 300 µg/L for everyone older than one (MDH). An MDH study found softeners can be an effective way to reduce manganese (same page).