How to Tell If You Have Hard Water: 5 Ways to Check

The quick version

You can usually tell you have hard water from what it leaves behind: white crust, spotty glasses and soap that won't lather. To know how hard it is, you need a number. The easiest places to get one are your water utility's annual report, PurityMap's city hard-water pages, or a home test strip.

Hardness is a comfort and plumbing issue. The US EPA sets no drinking-water standard for it, so a high number is not a health finding. The steps below are about finding out where you stand, not about a federal health limit.

1. Look for the signs around your home

Hard water tends to leave clues where water dries or gets heated:

• White or chalky crust on faucets, showerheads and the inside of kettles • Cloudy spots or film on glasses and dishes after the dishwasher • Soap scum on tubs and shower doors, and soap or shampoo that lathers poorly • Scale in a water heater, which can sometimes show up as popping or rumbling sounds when it heats

These signs are a good hint but not proof. Spots can also come from other dissolved solids, and a dishwasher's detergent and rinse settings change how glasses look. Use the signs to decide whether to check the number.

2. Try the soap-bottle test

Fill a clear bottle about a third full of cold tap water, add a few drops of plain liquid soap (plain castile soap is often suggested; detergents and body washes can lather regardless), cap it and shake hard.

Lots of stable bubbles and clear water underneath suggest softer water. Few bubbles and cloudy, milky water suggest harder water. This test can't give you a number, and results vary with the soap you use, so treat it as a rough check only.

3. Read your utility's water report

If you're on public water, your utility publishes a yearly Consumer Confidence Report (CCR). Many list hardness in a table of "secondary" or "other" parameters, as mg/L, ppm or grains per gallon. Some list calcium and magnesium separately instead, and some don't report hardness at all, because no federal rule requires it.

PurityMap pulls the hardness figures utilities report into its city hard-water pages, such as hard water in Phoenix, Tampa, San Antonio and Las Vegas, and the hard-water checker looks up your city in one step. When we don't have a reported number, the page says so instead of guessing.

Remember that a utility's figure is often a range or an average across its sources. If your city blends well water and river water, your tap can differ from the yearly figure.

4. Test your own tap

A hardness test strip usually gives a number within a few minutes. You dip the strip in a glass of tap water and match its color to the chart on the bottle. Strips read in steps, so they're good for placing your water in a band, not for an exact figure.

For a precise result, a certified laboratory can measure hardness, usually as part of a broader panel. That makes most sense if you're on a private well, where no utility report exists and federal monitoring doesn't apply, or if you're sizing a softener and want an exact grains figure. Note that a salt-free conditioner doesn't remove minerals, so a strip still reads hard after one is installed.

5. Ask your water heater or appliance installer

Plumbers and appliance installers often test hardness on site before fitting a water heater, dishwasher or softener, and many dishwasher manuals tell you to set a hardness level. If you've had work done recently, the reading may already be on an invoice. Ask which units it is in, because gpg and mg/L numbers look very different.

How to read the number you get

The US Geological Survey groups hardness into four bands (mg/L as calcium carbonate):

• Soft: 0 to 60 mg/L (up to about 3.5 gpg) • Moderately hard: 61 to 120 mg/L (about 3.5 to 7 gpg) • Hard: 121 to 180 mg/L (about 7 to 10.5 gpg) • Very hard: more than 180 mg/L (over about 10.5 gpg)

To convert, divide mg/L by 17.1 to get gpg, or multiply gpg by 17.1 to get mg/L. ppm and mg/L are the same for water.

If you land in the hard or very hard band and scale is a real nuisance, our guide to hard water vs soft water compares softeners, salt-free conditioners and filters, and the water softener buying guide covers sizing and salt costs. Is hard water safe to drink? Neither the EPA nor the WHO sets a health limit for hardness. That isn't a verdict on your tap: the hardness number tells you nothing about other substances in your water.

What to do next

Start with your city's hard-water page or the hard-water checker to see what your utility reports. If you want your own number, a hardness test strip is the cheapest way to get one; PurityMap lists the test kits we track below. Those links may be affiliate links: PurityMap may earn a commission from qualifying purchases, at no cost to you, and it never changes what we report.

If you also want to know about lead, PFAS or other contaminants, a hardness strip won't tell you. Open your city water report for the utility's records, and use a certified lab test for a private well.