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Hard water and water softeners: what to know

White crust on faucets, spotty dishes and soap that will not lather are signs of hard water. Here is how hardness is measured and what a softener does.

The short answer

Hard water carries dissolved calcium and magnesium. The USGS calls water over 120 mg/L hard and over 180 mg/L very hard. It leaves scale in water heaters and pipes. A water softener swaps those minerals for sodium. Ask your water utility for your hardness number before buying anything, and check local rules – some areas restrict softeners.

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What hard water is

The USGS explains that hardness is caused mainly by calcium and magnesium compounds. Its scale, measured as calcium carbonate: 0 to 60 mg/L is soft, 61 to 120 moderately hard, 121 to 180 hard, and over 180 very hard. Your water utility’s annual water quality report usually lists your hardness; if you are on a well, have it tested.

What it does

  • When hard water is heated, as in a water heater, calcium carbonate scale can form (USGS).
  • Scale can shorten equipment life, lower electric water heater efficiency and clog pipes (USGS).
  • Soap reacts with calcium to form soap scum, so soap lathers poorly (USGS).

Flushing the water heater tank as the manufacturer recommends helps – see no hot water.

How a water softener works

The Minnesota Department of Health explains that softeners remove calcium, magnesium and, to a lesser extent, iron, by ion exchange: water passes through resin beads loaded with sodium ions, which swap places with the hardness minerals. Keep enough salt in the brine tank, at or above the tank’s water level, MDH advises.

Sodium in softened water

The Vermont Department of Health notes that most conventional softeners add small amounts of sodium to the water. Minnesota’s health department advises anyone on a medically restricted sodium diet to talk with their doctor before regularly drinking softened water. Many homes leave the kitchen cold tap unsoftened for drinking.

Local rules

Softener brine goes into the sewer, and treatment plants that do not remove salt pass it on to rivers, where too much can harm downstream crops, the Los Angeles County Sanitation Districts explain. Some areas ban automatic (self-regenerating) softeners – in California’s Santa Clarita Valley, installing them has been prohibited since 2003. Ask your city or a local plumber what is allowed before you install one.

Getting one installed

Ask how the plumber sized the unit for your hardness and household, where the brine discharge will go, whether a bypass valve and an unsoftened drinking tap are included, and what permit is needed. Our hiring guide has the questions to ask every plumber.

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Questions

What counts as hard water?

The USGS classifies water over 120 mg/L (as calcium carbonate) as hard and over 180 mg/L as very hard. 0 to 60 mg/L is soft.

Does a water softener add salt to drinking water?

Most conventional softeners add a small amount of sodium. People on a medically restricted sodium diet should ask their doctor before regularly drinking softened water.

Is hard water bad for a water heater?

It can be. The USGS says heated hard water forms scale, which can shorten equipment life and lower electric water heater efficiency.

Are water softeners allowed everywhere?

No. Some areas restrict or ban automatic softeners because of salty discharge – California’s Santa Clarita Valley has prohibited installing them since 2003. Check local rules.

Related guides

No hot water? What to check before you callNo hot water usually comes down to fuel, a safety control doing its job, or a heater near the end of its life. Here is how to narrow it down safely.Tank vs tankless water heater: how to chooseReplacing a water heater is the moment to choose the type. Here is how storage tanks, tankless units and heat pump water heaters differ, using figures from the U.S. Department of Energy.Lead pipes and lead in water: how to check and what to doHomes built before 1986, especially in older cities, may have lead pipes or a lead service line. Here is how to find out and how to lower your exposure in the meantime.

Sources

Facts and figures in this guide come from these official and manufacturer sources, checked October 2026:

  1. USGS Water Science School – Hardness of water
  2. Minnesota Department of Health – Water softeners (PDF)
  3. Vermont Department of Health – Sodium and chloride in drinking water
  4. Los Angeles County Sanitation Districts – Automatic water softeners

Updated October 2026 by the Plumbers Pages editorial team. General information for homeowners, not professional advice – codes and equipment differ, so follow your product’s manual and local rules. When gas, electricity, sewage or anyone’s safety is involved, call 911, your utility or a licensed plumber. How we write our guides · Plumbing glossary

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