Water Softeners for Well Owners: How They Work

A water softener is a tank of resin beads that trades the calcium and magnesium in your water for sodium (or potassium), then flushes the captured hardness down the drain with a salt brine. The Minnesota Department of Health says a softener may be worth it once hardness passes 7 grains per gallon (120 mg/L); below that, Penn State Extension notes, scale and soap film are usually minor. On a private well, test hardness and iron first, because iron decides what kind of equipment you need and how large it has to be.

How a water softener works

Household softeners are ion-exchange units. The resin, usually sulfonated polystyrene beads, starts out loaded with sodium. As hard water flows through, calcium and magnesium cling to the beads and the loosely held sodium is released into the water (NebGuide G1491). The result is water in the “soft” range — under 1 grain per gallon, which is the definition the Water Quality Association cites from NSF/ANSI 44 and NSF/ANSI 330.

Ion exchange removes nearly all calcium and magnesium. According to the same NebGuide, a softener can also take out as much as 5–10 ppm of dissolved iron and manganese, depending on the manufacturer’s rating. It does not remove bacteria, hydrogen sulfide, sand, lead, nitrate or pesticides, so a softener is never a substitute for a well water test and the treatment that test calls for.

How hard is hard?

Hardness is reported either in milligrams per liter (mg/L, the same as ppm) or grains per gallon (gpg). One gpg equals 17.1 mg/L. Nebraska Extension and WQA use this scale:

Agencies draw the “soften” line in slightly different places. Minnesota uses 7 gpg (120 mg/L). Connecticut’s Department of Public Health says its historic guideline recommended softening above 150 ppm (8.8 gpg), and notes there is no health-based standard for hardness at all.

Grains, capacity and regeneration

A softener’s size is its grain capacity: how many grains of hardness the resin can hold before it has to be recharged. Industrial water-treatment supplier Solenis gives the usual benchmark as about 30,000 grains per cubic foot of resin when it is regenerated with 15 lb of salt per cubic foot; lower salt doses leave less capacity but use less salt. Connecticut DPH uses the same 30,000-grain figure and works an example: a family of four using 300 gallons a day of 100 ppm water would need one cubic foot of resin regenerated about every 17 days.

Regeneration flushes the resin with brine, pushing the calcium and magnesium out to the drain. NebGuide G1491 says it takes 60 to 120 minutes and about 50 gallons of water — roughly one load in an older washing machine. Older units start regeneration on a timer; demand-initiated regeneration (DIR) units meter the water used (or sense the resin) and regenerate only when capacity is spent, which saves salt and water.

To compare efficiency, look for a rating under NSF/ANSI 44. A softener earns an efficiency rating if it removes at least 3,350 grains of hardness per pound of salt and uses no more than 5 gallons of regeneration water per 1,000 grains removed, at a stated salt setting (WC&P, 2013). Our water softener size calculator shows how household size, hardness and iron add up to a capacity.

Salt or potassium chloride

Sodium chloride is the standard regenerant. Softening adds sodium to the water: about 8 mg/L for each gpg of hardness removed, per NebGuide G1491, so 10 gpg water ends up near 80 mg/L sodium. Connecticut DPH puts it as 46 ppm sodium added per 100 ppm of hardness removed. People on sodium-restricted diets are advised to account for this and talk to their physician; a common workaround is a cold-water line to the kitchen tap that bypasses the softener.

Potassium chloride can replace salt. Connecticut DPH says it adds about 76 ppm potassium per 100 ppm of hardness removed instead of sodium. The trade-offs, per Nebraska Extension: it costs more, can be harder to find, and holds more tightly to the resin, so it regenerates less efficiently and you need more of it. Check that your softener’s manufacturer allows it before switching.

Does a private well need a softener?

Start with a lab test that reports hardness, iron, manganese and pH. Then:

• Hardness under about 7 gpg: Minnesota and Penn State guidance suggests a softener is optional.
• Hardness above 7 gpg with low iron: a standard softener is the conventional fix.
• Dissolved (clear-water) iron: a softener can remove some, up to its rating. Penn State Extension warns that iron already oxidized — by air or chlorine — clogs the resin, and NebGuide G1491 says iron above 5 ppm reduces a softener’s effectiveness. Plan on an iron filter ahead of the softener in those cases; see iron in well water.
• Sediment: sand and silt also cut softener performance (NebGuide G1491), so a sediment filter usually goes first.

You rarely need to soften everything. The Minnesota Department of Health notes most households soften showers, sinks and laundry and leave toilets, hose bibs and outdoor taps on hard water. Fewer softened gallons means a smaller unit and less brine.

Downsides to weigh

Minnesota’s Health Department lists these trade-offs: over-softened water can corrode pipes and raise lead and copper levels; softened water carries extra sodium; the unit needs regular testing and maintenance; the salt ends up in the environment; and regeneration water is waste. If your home has new copper plumbing, Minnesota advises not running the softener for the first few weeks so a protective mineral layer can form.

If you are on a septic system, the WQA and the National Onsite Wastewater Recycling Association recommend a high-efficiency or demand-initiated unit. The research and the state rules are covered in septic safe water softeners.

Softening guides in this section

• Water softener size calculator — grain capacity from household size, hardness and iron, with the formula shown.
• Water softener installation cost — unit, labor, plumbing and permit ranges with the source for each.
• Water softener vs water conditioner — what salt-free devices do and the test standards behind their claims.
• Septic safe water softener — what the studies found about brine and septic systems.
• Best water softener for well water — picks sized for iron and well conditions.
• Best water softener — the wider field compared on capacity and efficiency.
• Best salt-free water softener — conditioners compared, with their test claims.

Already have a softener that isn’t keeping up? Start with water softener problems.