Water hardness

What water hardness is

Water hardness is a measure of the dissolved minerals in your water, mainly calcium and magnesium. Water picks these up as it moves through the ground, and the more it carries, the harder it is.

The USGS classifies hardness by the concentration of these minerals, measured in milligrams per liter or in grains per gallon. Water under 60 milligrams per liter is considered soft. From 61 to 120 is moderately hard, 121 to 180 is hard, and anything above 180 is very hard. One grain per gallon equals about 17 milligrams per liter, which is the unit most water-softener companies use. The higher the number, the more mineral your water holds and the more visible its effects become around the house.

Where hardness comes from

Hard water is a product of geology. As rain and snowmelt move through soil and rock, they dissolve minerals from the ground, and the type of rock decides how much they pick up.

Limestone, chalk, and dolomite are the main culprits. These rocks are rich in calcium and magnesium, and water flowing through them dissolves those minerals along the way, the USGS reports. This is why hardness varies so sharply by region. The middle of the country, including much of the Midwest and Southwest, sits on mineral-rich rock and tends toward hard or very hard water. Parts of the Northeast, Pacific Northwest, and Southeast sit on different geology and tend toward softer water.

The source matters too. Groundwater pulled from wells and aquifers spends far more time in contact with rock than surface water, so it dissolves more mineral and runs harder. Surface water from rivers, lakes, and reservoirs moves faster and touches less rock, so it tends to be softer. This is why a home on a private well often has harder water than a neighbor on a public surface supply.

What hardness does, and does not do, to your health

Hard water is safe to drink. The World Health Organization has found no convincing evidence that water hardness causes adverse health effects, and the USGS classifies it as a nuisance rather than a health concern. The calcium and magnesium that make water hard are the same minerals your body needs, and some studies suggest hard water may contribute a small share of daily intake.

The effects people notice are cosmetic and physical, not medical. Hard water can leave skin feeling dry and hair feeling filmy, because the minerals react with soap to leave a residue that plain rinsing does not fully clear. It does not cause skin disease, though people with eczema sometimes report that hard water aggravates the condition. There is no CDC guidance to avoid hard water for health reasons, and no federal drinking water limit exists for hardness, because none is needed to protect people. If your water is hard, the problem is what it does to your home, not what it does to you.

What hardness does to plumbing and appliances

This is where hard water earns its reputation. When hard water is heated or left to sit, the dissolved calcium and magnesium come out of solution and form a chalky deposit called scale. That scale builds up inside pipes, water heaters, and any appliance that heats or holds water.

The cost adds up over time. Scale narrows the inside of pipes, reduces water flow, and coats the heating elements in water heaters, which forces them to work harder and use more energy. A study by New Mexico State University for the Water Quality Research Foundation found that scale buildup can cut the efficiency of a water heater significantly and shorten its working life. Dishwashers, washing machines, coffee makers, and ice machines all wear out faster when scale collects inside them. The same deposits leave the spots on glassware and the crusty white ring on faucets and showerheads.

Soap is the other casualty. Hard water reacts with soap to form a sticky curd, the familiar soap scum on tubs and shower doors, and it keeps soap and detergent from lathering well. That means you use more soap, more detergent, and more shampoo to get the same result, and laundry can come out stiff or dingy as mineral residue settles into the fabric.

What a household can do

Test your water first, because the right response depends on how hard your water actually is. Many public water systems list hardness in their annual Consumer Confidence Report, and inexpensive test strips or a certified lab can measure it for a well. Knowing your number, in grains per gallon or milligrams per liter, tells you whether hardness is worth treating at all.

Decide whether treatment makes sense for your situation. Because hard water is not a health risk, softening is a choice about convenience and protecting your appliances, not safety. A whole-house water softener is the most common fix. It uses ion exchange to swap the calcium and magnesium for sodium, which stops scale from forming. That process adds a small amount of sodium to the water, so people on low-sodium diets sometimes install a softener that uses potassium instead, or leave one tap unsoftened for drinking and cooking. Salt-free conditioners are another option that changes how minerals behave without removing them, though they do not soften water in the traditional sense.

Manage the effects without a system if your water is only moderately hard. Wipe down shower doors and faucets to prevent scale from setting, run vinegar through a coffee maker or dishwasher to dissolve buildup, and use a rinse aid in the dishwasher to cut spots. Descale a showerhead by soaking it in vinegar. Set your water heater to a lower temperature, since hotter water forms scale faster. For laundry, adding a bit more detergent or a water-softening laundry additive helps clothes come out cleaner in hard water.