Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A water hardness test strip gives you a fast, rough number for how much dissolved calcium and magnesium is in your tap water. Dip a strip, wait, and match its color to the chart on the container to get a reading in milligrams per liter (mg/L), parts per million (ppm), or grains per gallon (gpg). This page walks through collecting a fair sample, running the strip correctly, and reading the color chart without guessing between two blocks. It also explains what the number means, using the U.S. Geological Survey's own classification for soft, moderately hard, hard, and very hard water.
Hard water is not a health hazard — it just carries more dissolved minerals, which can leave scale in a kettle, a coffee machine, or a steam iron, and can make soap harder to lather. This page tells you how hard your water is and what that number means. It does not size a water softener, recommend a softening chemical dose, or replace a certified laboratory test. A test strip is accurate enough to plan maintenance; for a softener purchase or a suspected water quality problem, use a laboratory test or ask your water utility.
Necessary equipment
| Item | Note |
|---|---|
| Timer or clock | The reading time is different for each product. |
| Clean cup or glass | Use a container with no soap residue. |
| Pen and paper, or a phone optional | Record the date and the result of the test. |
| Water hardness test strip material | The colour chart on the container matches only that container's own strips. |
Start
Estimated 2 min to 2 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Read the instructions on the test strip container.<1mReport a problem with step 1, Start
- The dip time and the reading time are different for each product.
- The colour chart matches only its own container.
DO NOT USE AN EXPIRED TEST STRIP.
An expired strip can give a wrong result.
- Examine the expiration date on the container.<1mReport a problem with step 2, Start
- Gather a clean cup, a timer, and paper for notes.<1mReport a problem with step 3, Start
Collect the water sample
Estimated 2 min to 2 min
- Pick a cold-water tap with no filter fitted.<1mReport a problem with step 1, Collect the water sample
- Run the tap until the water feels consistently cold.<1mReport a problem with step 2, Collect the water sample
- Fill the cup with water from the tap.<1mReport a problem with step 3, Collect the water sample
- Note whether the sample is from before or after a softener.<1mReport a problem with step 4, Collect the water sample
- A sample from before a softener tests the water supply.
- A sample from after a softener tests the softener's performance.
Run the test
Estimated 1 min to 2 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
DO NOT TOUCH THE TEST PAD OF THE STRIP.
A dirty or oily finger can cause a wrong reading.
CLOSE THE CONTAINER LID IMMEDIATELY AFTER YOU REMOVE A STRIP.
Moisture in the air can spoil the strips left in the container.
- Remove one test strip from the container.<1mReport a problem with step 1, Run the test
- Close the container lid.<1mReport a problem with step 2, Run the test
- Dip the test strip in the water sample.<1mReport a problem with step 3, Run the test
- Follow the dip time on your own container.
- Remove the strip from the water.<1mReport a problem with step 4, Run the test
- Hold the strip level while you wait.<1mReport a problem with step 5, Run the test
- Do not blot or wipe the test pad.
- Follow the reading time on your own container.
Read the colour chart
Estimated under a minute
- Compare the colour of the test pad to the chart.<1mReport a problem with step 1, Read the colour chart
- If your result is between two colour blocks, choose the closer block.<1mReport a problem with step 2, Read the colour chart
- Read the number next to the colour block that matches.<1mReport a problem with step 3, Read the colour chart
- Your container states its own unit.
- One choice is milligrams per litre.
- Another choice is parts per million.
- A third choice is grains per gallon.
Classify the result
Estimated under a minute
Source: Hardness of Water · tier 1 · accessed 2026-08-04
Source: Hardness of Water · tier 1 · accessed 2026-08-04
Source: Hardness of Water · tier 1 · accessed 2026-08-04
Source: Hardness of Water · tier 1 · accessed 2026-08-04
Source: NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically · tier 1 · accessed 2026-08-04
- Convert a grains-per-gallon result to milligrams per litre.<1mReport a problem with step 1, Classify the result
- Apply the conversion factor given on this page.
- Match your result to a classification on this page.<1mReport a problem with step 2, Classify the result
- This page states ranges in milligrams per litre.
- Parts per million and milligrams per litre are the same reading.
- The classifications are soft, moderately hard, hard, and very hard.
Record the result
Estimated under a minute
- Record the date and the hardness result.<1mReport a problem with step 1, Record the result
- Compare your result with the water quality report from your utility.<1mReport a problem with step 2, Record the result
- Utilities often publish this report once a year.
- Repeat this test after a change in your water supply or your softener.<1mReport a problem with step 3, Record the result
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- water hardness
- Also called: hard water, how hard is my water, water hardness level, is my water hard or soft
- grains per gallon
- Also called: gpg, grains per gallon (gpg), hardness grains, grains hardness
- water hardness test strip
- Also called: hardness test strip, limescale test strip, water hardness test kit, hard water test strip, dip strip
- calcium carbonate equivalent
- Also called: CaCO3, hardness as calcium carbonate, mg/L as CaCO3, ppm as CaCO3
- water softener
- Also called: softener system, ion exchange softener, salt-based softener
- limescale
- Also called: scale, mineral buildup, white residue, hard water stains
When to use a professional
This procedure gives a rough hardness number for home use. It does not replace a certified laboratory water test. Hard water is not a health hazard, so this page does not cover water safety or contamination.
This page does not size a water softener. It does not state a chemical dose for a softener. Consult a water treatment professional before you buy or install a softener. Contact your water utility, or a certified laboratory, if you suspect a water quality problem.
Common questions
How do I know if my water is hard or soft?
The most direct way is a home water hardness test strip: dip it in a water sample, wait the time printed on the container, and match the color to the chart. Your result will read in milligrams per liter (mg/L), parts per million (ppm), or grains per gallon (gpg). The U.S. Geological Survey classifies water as soft, moderately hard, hard, or very hard based on the mg/L reading, as calcium carbonate — this page states those ranges. If you'd rather not test it yourself, your water utility's annual water quality report often lists the supply's hardness.
What counts as 'hard water,' and what does my number mean?
Using the U.S. Geological Survey's classification, water from 0 to 60 mg/L (as calcium carbonate) is soft, 61 to 120 mg/L is moderately hard, 121 to 180 mg/L is hard, and anything above 180 mg/L is very hard. If your test strip reports grains per gallon instead, this page's conversion factor (about 17.1 mg/L per grain, computed from NIST's exact unit definitions) lets you convert your reading before comparing it. For example, 3.5 gpg works out to about 60 mg/L — right at the soft/moderately-hard boundary. Hardness is a matter of scale and soap performance, not a safety threshold.
Is hard water unsafe to drink?
No. The U.S. Geological Survey states plainly that hardness 'is a property of water that is not a health concern, but it can be a nuisance.' The nuisance is scale and reduced soap performance: hard water needs more soap or detergent to clean effectively, and when heated it can leave calcium carbonate deposits that clog pipes and shorten equipment life. That's the practical reason to test — knowing your number helps you plan descaling and softening maintenance, not protect your health. If you have a specific water quality concern, such as taste, odor, or a suspected contaminant, contact your water utility or a certified laboratory rather than relying on a hardness strip.
What's the difference between ppm, mg/L, and grains per gallon (gpg)?
Parts per million (ppm) and milligrams per liter (mg/L) are essentially the same reading for water hardness — GE Appliances' own support page states the equivalence directly: '1 grain per U.S. gallon (GPG) = 17.1 milligrams per liter (mg/L) = 17.1 PPM.' Grains per gallon is an older unit still common in the water-softener industry in North America, while mg/L and ppm are the units labs and agencies like USGS typically use. This page publishes its classification in mg/L and gives the grain-to-mg/L conversion factor, computed from NIST's exact definitions of the grain and the U.S. gallon, so you can convert either way.
How accurate is a water hardness test strip?
A dip-and-read test strip is a quick screening tool, not a laboratory-grade measurement — it's accurate enough to tell you which hardness band you're in and to plan maintenance like descaling. Reading it correctly matters: use the dip time and reading time printed on your own container, hold the strip level, and read the color promptly, since lighting and timing both affect the color match. For a precise number, such as before you buy or size a water softener, use a certified laboratory test instead.
My test says my water isn't 'very hard' — why is there still scale in my kettle?
Any hardness above zero means some dissolved calcium and magnesium in the water. USGS notes that heating hard water can leave calcium carbonate deposits, and scale builds up gradually — daily use in a kettle, a coffee machine, or a steam iron can show visible buildup well before a supply reaches the 'hard' range on this page. See this site's descaling pages for the kettle, the coffee machine, and the steam iron for how the buildup relates to your test result.
How often should I test my water hardness?
There's no official interval — this is a matter of household habit, not a published standard. Many people test once, note the number, and retest only if their water supply changes (a new well, a municipal source change) or after a water softener is installed or serviced. If you're troubleshooting more scale than usual, a fresh test tells you whether your supply has changed or whether it's simply time to descale.
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Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1Hardness of Water
- Tier 1NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically
- Tier 1Definition of Grains Per Gallon
Revision history
Current version 1 · updated 2026-08-04 · next review due 2027-08-04
- v1 · 2026-08-04First draft. The soft/moderately-hard/hard/very-hard classification in mg/L as calcium carbonate, the health/nuisance framing, and the scale-formation facts in the summary and FAQ are sourced from the U.S. Geological Survey Water Science School page 'Hardness of Water', fetched and read directly at usgs.gov on 2026-08-04 (HTTP 200). The grains-per-gallon-to-mg/L conversion factor (17.1) is computed from two exact unit definitions in NIST Special Publication 811, Appendix B.8 (fetched and read directly, updated by NIST 2025-08-18): 1 grain = 64.79891 mg and 1 U.S. gallon = 3.785412 L. That NIST source, not the undated GE Appliances page, is cited as the specification's source_id for that reason; GE Appliances' own support page (also fetched and read directly) is staged and cited only as corroboration of the same rounded figure and for the ppm/mg/L equivalence quoted in FAQ 4. Two values are deliberately left unverified with no digit in the published value: the dip time and reading time for a test strip (multiple manufacturers' own product pages, checked during research, give dip times from about 1 to 5 seconds and reading waits from immediate to about 1 minute for different water-test-strip products, so no single figure is honest to publish as a page-wide value), and the storage/shelf-life condition for unused strips. Neither hardness itself nor any value on this page appears in config.json's safety_critical_specs list; the U.S. Geological Survey source states directly that hardness 'is not a health concern.' No competitor page was read or drafted from at any point (brief 1.5); the backlog entry's discovery_source records only that a topic sweep found demand for this subject. This page deliberately does not size a water softener or state a chemical dosing figure, per the backlog entry's own scope note. Sources are staged in data/sources-additions-measure-water-hardness-with-a-test-strip.json and are not yet admitted to data/sources.json; check 3 will hold this record until scripts/sources_admit.py runs.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.