Signs you have hard water

By Ajay Singh. Updated November 10, 2026.

The surest signs are white or gray crust where water dries (on faucets, shower heads and the inside of the kettle), spots and film on glasses, and soap or shampoo that won't lather well. Signs only tell you it's there, though. To know how hard your water is, you need a number from your water utility's report or a test.

What you'll notice around the house

• White or gray scale. Penn State Extension says hard water causes gray or white deposits when water is heated. Look inside the kettle and coffee maker, around faucet aerators, and on shower heads.
• Scale on pots. Penn State lists scale on pots alongside soap films and detergent curds as the classic signs.
• Spots on glassware. The Minnesota Department of Health lists mineral spots on glassware as one of the problems softening prevents. Nebraska Extension calls it unsightly film on glass and crystal.
• Soap scum and ring marks. Hard water leaves soap films in sinks and tubs and detergent curds in washing machines, according to the Minnesota Department of Health.
• Poor lather. The Connecticut Department of Public Health puts it simply: hard water doesn't lather easily and makes laundry harder. The USGS notes that hard water needs more soap and detergent for laundry and washing.
• A film on your skin after washing. Penn State mentions soap films on skin.
• Clogged shower heads and scaled fixtures. Nebraska Extension lists mineral buildup on plumbing fixtures, including water heaters.

What it does to your water heater

Scale builds up wherever water is heated, and the water heater heats the most. The best-known study on this was done by Battelle for the Water Quality Association, the water treatment industry's trade group, which funded it. As reported in Contractor magazine:

• Gas storage water heaters on unsoftened hard water fell from 70.4% to 67.4% efficiency over the equivalent of two years of use, while those on softened water held steady.
• Tankless heaters on hard water needed deliming after the equivalent of 1.6 years, by which point efficiency had dropped from 80% to 72%.
• Low-flow shower heads on hard water clogged after an average of 3,203 gallons.

Bear in mind who paid for it, and that the tests were accelerated. Still, the direction is clear: scale makes heaters work harder.

What the numbers mean

Hardness is mostly calcium and magnesium, and it's measured either in milligrams per liter (mg/L, the same as parts per million) or in grains per gallon (gpg). One grain per gallon is 17.1 mg/L, the factor Connecticut's public health department uses.

This five-band scale is from Nebraska Extension, which attributes it to the US Department of the Interior and the Water Quality Association; Penn State uses the same bands. The USGS uses a simpler four-band version: soft up to 60 mg/L, moderately hard 61 to 120, hard 121 to 180, and very hard above 180.

The Minnesota Department of Health suggests that above 7 gpg (120 mg/L) you might want a water softener.

How to get your hardness number

• On city water: community water systems have to send customers an annual drinking water quality report, the Consumer Confidence Report, by July 1 each year, according to the EPA. Many list hardness, though it isn't required. If yours doesn't, call the utility and ask; they usually know.
• On a private well: get it tested. Ask for hardness to be included in a lab test; the same test can tell you about iron, manganese and pH, which all affect what treatment you need. The CDC recommends testing a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH, through a state-certified lab. Your state or local health department can tell you what else to test for where you live.
• Home test strips can show roughly whether water is hard, but for choosing equipment, especially on a well, a lab result is the one to rely on.

When the stains aren't white

Hardness leaves white or gray deposits. Other colors mean something else is in the water:

• Orange, red or brown stains usually mean iron. The EPA's guideline for iron is 0.3 mg/L. See iron in well water.
• Black or dark brown stains point to manganese, with an EPA guideline of 0.05 mg/L.
• Green stains can mean low-pH, acidic water, which the University of Nebraska links to treatment with a calcite filter or soda ash.

What to do next

• Once you have a number, the softener size calculator tells you what capacity you'd need.
• Deciding between salt and salt-free? Read softener vs conditioner.
• Ready to compare models? See water softeners compared.