How to Test Water Hardness at Home (Test Kits Compared)

Hard water is easy to suspect and hard to put a number on. You see white crust on faucets, spots on glasses, and soap that won't lather. But to fix it, or to size a water softener, you need a real number.

This guide compares the main types of water hardness test kits, shows you how to read results in gpg and ppm, and explains how to turn your number into a softener size. It also covers when a home kit isn't enough.

Before you start: A hardness kit only measures hardness. It won't tell you if water is safe to drink. If you use a private well, the CDC recommends a yearly test for bacteria, nitrates, pH, and total dissolved solids at a state-certified lab (CDC).

What is water hardness?

Water hardness is the amount of dissolved calcium and magnesium in your water. Water picks these minerals up as it moves through rock and soil. The USGS notes that hardness is usually reported as an amount of calcium carbonate (USGS).

Hard water is mainly a nuisance. The Water Quality Association (WQA) lists these common symptoms (WQA):

• Stiff, dingy laundry
• Mineral deposits on dishes and glassware
• High soap use and a need for fabric softener
• Extra work to remove soap curd from tubs and showers
• Higher energy costs, possibly from scale in pipes and on appliances

The WQA also says calcium and magnesium cause most of the scaling in pipes and water heaters. That's why many people test hardness before they decide on a softener.

What types of water hardness test kits are there?

There are four main ways to test hardness, plus one tool that people often mistake for a hardness test. Here is how they compare.

Sources: UNL Extension G1491; Hach (manufacturer); Aquatell (retailer).

Test strips

Test strips are the simplest option. You dip a strip in a water sample and compare the color pad to a chart on the bottle. The result is a range, not an exact number.

University of Nebraska–Lincoln Extension says home test kits and dip strips vary in accuracy, and lab tests are more reliable (UNL Extension). Strips are still useful for a fast answer to "is my water hard?" and for spot-checking whether a softener is working.

Tips for better strip results:

• Follow the kit's instructions for dip time and reading time exactly.
• Compare the color to the chart in good light.
• Test water from a cold tap that hasn't passed through a softener or filter, unless you are checking that device.
• Check the expiration date and storage notes on the bottle.

Drop titration kits

A drop titration kit gives a more exact number. You fill a tube to a set line, add an indicator that colors the water, then add a test solution one drop at a time. You count the drops until the color changes.

For example, one manufacturer's total hardness kit, the Hach Model 5-B, uses EDTA titration. The sample turns from red or pink to blue when the test is done. Per Hach, each drop equals 1 gpg (17.1 mg/L), with a range of 1 to 30 gpg and about 100 tests per kit (Hach). Other kits work the same way, but check the drop value in your kit's instructions.

How to run a drop test:

1. Rinse the sample tube with the water you are testing.
2. Fill the tube to the marked line.
3. Add the indicator (a tablet, powder, or drops, depending on the kit).
4. Add the test solution one drop at a time, swirling after each drop.
5. Stop when the color changes fully, and count the drops.
6. Convert drops to gpg using your kit's instructions.

Titration takes a few minutes. It's the best home method if you plan to size or program a softener.

Digital meters

Digital meters are tempting because they give a number on a screen. But read the label carefully. Many low-cost "water quality" pens are TDS meters, and a TDS meter is not a hardness meter. If a device does measure hardness, follow its calibration steps.

Why a TDS meter can't measure hardness

TDS stands for total dissolved solids. A TDS meter measures the water's electrical conductivity and estimates all dissolved material from it. Hardness is only part of that total.

Aquatell, a water treatment retailer, explains two problems (Aquatell):

• TDS includes much more than hardness, so the TDS number will be higher than your hardness.
• A TDS meter can't check a softener. A softener swaps calcium and magnesium for sodium. Sodium carries the same electrical charge, so hard and softened water read about the same.

A TDS meter is useful for other jobs, like checking a reverse osmosis system. The EPA's secondary (non-enforceable) guideline for TDS is 500 mg/L (EPA). Just don't use it to measure hardness.

Certified lab tests

A lab test is the most reliable option. UNL Extension recommends confirming hardness with an approved lab before a major purchase, such as a softener, and retesting after installation.

A lab test also checks things a hardness kit can't, like iron. Iron matters for softener sizing, as you'll see below. If you have a well, test it at a lab anyway. A combined panel saves time.

HomeGuide reports that professional water testing costs about $100 to $300 (HomeGuide).

How do you read hardness results in gpg and ppm?

Hardness is reported in two main units:

• Grains per gallon (gpg), common for softeners in the U.S.
• Parts per million (ppm) or milligrams per liter (mg/L). These are the same for water.

To convert: 1 gpg is about 17.1 ppm (WQA). Divide ppm by 17.1 to get gpg. Multiply gpg by 17.1 to get ppm.

Conversion: ppm ÷ 17.1 = gpg.

What counts as hard water?

Penn State Extension uses this scale (Penn State Extension):

Source: Penn State Extension, Water Softening.

The USGS uses a slightly simpler scale: 0 to 60 mg/L is soft, 61 to 120 is moderately hard, 121 to 180 is hard, and over 180 is very hard (USGS).

The WQA notes that standards NSF/ANSI 44 and NSF/ANSI 330 define soft water as less than 1 gpg (17.1 mg/L). That is a handy target when checking a softener.

Do you need a softener?

Penn State says water under about 7 gpg probably won't cause major scaling problems. Above that, scale tends to build up in pipes, water heaters, and fixtures. Whether to soften is your call. It depends on how much the scale bothers you and your budget.

If you're on a low-sodium diet, note that UNL Extension says softening adds about 8 mg/L of sodium per gpg removed. Water at 10 gpg would gain about 80 mg/L.

How do you use your results to size a water softener?

Your hardness number is the starting point for choosing a softener's capacity, measured in grains. Here is the basic math, based on guidance from a softener manufacturer and an equipment distributor.

Step 1: Adjust for iron

Dissolved iron uses up softener capacity, too. Nelsen Corp, an equipment distributor, recommends a compensated hardness (Nelsen Corp):

Compensated hardness (gpg) = hardness (gpg) + (4 × dissolved iron in ppm)

So 10 gpg of hardness with 1 ppm of iron becomes 14 gpg for sizing. Nelsen notes most softeners are rated for only about 2 ppm of dissolved iron. Higher iron usually needs separate treatment.

Step 2: Estimate daily grains

Multiply your hardness by your daily water use. Aquasana, a manufacturer, uses this formula with an assumption of 82 gallons per person per day (Aquasana):

People × gallons per person per day × gpg = grains per day

Example: 4 people × 82 gallons × 10 gpg = 3,280 grains per day.

Step 3: Pick a capacity

Divide the softener's capacity by your daily grains to see how often it would regenerate. In Aquasana's example, a 32,000-grain softener at 3,280 grains a day regenerates about every 9.75 days.

Nelsen suggests sizing for regeneration every few days and rounding up to the next size. It also notes that capacity at an efficient salt setting is lower than the maximum rating. For example, a unit sold as 32,000 grains may give closer to 24,000 at an efficient setting.

Sources: Nelsen Corp (distributor); Aquasana (manufacturer); UNL Extension.

Aquasana warns that an undersized softener can let hard water through, while an oversized one can waste money. UNL Extension adds that sizing depends on hardness, water use, and flow rate.

Ready to shop? Our best water softener buyer's guide explains features, certifications, and sizing in more detail. Our water softener cost guide covers what you'll pay.

What a hardness test kit doesn't tell you

A hardness kit answers one question. It doesn't tell you about other common problems, and some of them look like hardness at first.

Sources: Penn State Extension; CDC.

Penn State Extension notes that iron and manganese give water a metallic taste and cause staining (Penn State Extension). Both can also affect which softener or filter you need.

City water users: HomeGuide points out that you can check your water utility's Consumer Confidence Report, which is published each year (HomeGuide). Your own tap test still matters, since it measures the water that actually reaches your home.

Well owners: A hardness kit is not a safety test. The CDC recommends testing a private well every year for bacteria, nitrates, pH, and total dissolved solids (CDC). The EPA also suggests checking the visible parts of your well for problems like a cracked casing or a broken cap (EPA).

How often should you test water hardness?

• Before buying a softener: Test at home, then confirm with a lab.
• After installing a softener: UNL Extension recommends retesting to confirm it works.
• Now and then with a softener: A quick strip test of softened water catches problems early.
• When hard-water signs return: Spots or scale coming back can mean a softener problem.
• Well owners: Add hardness to your yearly lab test so you have a fresh number on record.

If your softened water tests hard again, our water softener repair guide walks through the usual causes, like a salt bridge or a clogged injector.

Common hardness testing mistakes

• Using a TDS meter. It doesn't measure hardness.
• Testing softened water to size a softener. Test the hard water, from a tap before the softener or with the softener in bypass.
• Ignoring iron. It changes the size you need.
• Ignoring the instructions. Dip and reading times matter for strips, and drop values vary by kit.
• Skipping the lab for a well. A hardness kit tells you nothing about safety.

The bottom line

Use strips to find out if your water is hard. Use a drop titration kit to get a number. Confirm with a lab before you buy a softener, especially on a well. Then use your gpg, iron level, and household size to choose a softener capacity.

For more on testing, browse our water testing guides. If you're on a well, our well water filtration systems guide explains what to test and how to treat it. You can also read how we research our guides.

FAQ

Sources

• CDC, Guidelines for Testing Well Water (accessed Oct 31, 2026)
• USGS Water Science School, Hardness of Water (accessed Oct 31, 2026)
• Water Quality Association, Scale Deposits (hardness) (accessed Oct 31, 2026)
• Penn State Extension, Water Softening (updated Sep 8, 2025; accessed Oct 31, 2026)
• Penn State Extension, Iron and Manganese in Private Water Systems (accessed Oct 31, 2026)
• University of Nebraska–Lincoln Extension, Drinking Water Treatment: Water Softening (Ion Exchange), G1491 (accessed Oct 31, 2026)
• U.S. EPA, Secondary Drinking Water Standards: Guidance for Nuisance Chemicals (accessed Oct 31, 2026)
• U.S. EPA, Protect Your Home's Water (private wells) (accessed Oct 31, 2026)
• Hach (manufacturer), Total Hardness Test Kit, Model 5-B (accessed Oct 31, 2026)
• Aquatell (retailer), How to Test Water Hardness With a TDS Meter (accessed Oct 31, 2026)
• Aquasana (manufacturer), How to Size a Water Softener (accessed Oct 31, 2026)
• Nelsen Corp (equipment distributor), Softener Sizing (accessed Oct 31, 2026)
• HomeGuide, Water Filtration System Cost (updated Sep 17, 2025; accessed Oct 31, 2026)

This guide is based on public agency guidance, university extension research, and manufacturer and retailer information, which is labeled as such. Filtiva has not hands-on tested any test kits. Always follow your kit's instructions.

Filtiva earns commissions from some links on this page at no extra cost to you. Commissions never change our criteria. We have not hands-on tested the products mentioned; all facts come from the linked sources, checked on October 31, 2026.