Hardness
Dissolved calcium and magnesium. Not a health issue, but it decides scale, soap and how your water feels.
- Safe range
- 0 – 500 mg/L
- Ideal range
- 60 – 120 mg/L
- Measured in
- mg/L
What it is
Hardness is the amount of dissolved calcium and magnesium the water carries, picked up as it moves through rock and soil. Hard water is entirely normal in much of the world and is a geological fact about where you live rather than a defect.
Why it matters
Hardness is not a health parameter, and it is worth being clear about that before spending money on it. What it costs you is practical: scale in kettles, coffee machines and water heaters, more soap and detergent to get the same result, spotted glassware, and that squeaky-versus-slippery difference in the shower. Those are real costs, but they are appliance and comfort costs.
How to measure it
Your utility publishes this, and a cheap titration kit will tell you what a softener is actually doing. Scale in the kettle and soap that will not lather are the free version of the same information.
Your utility's annual water quality report
- How trustworthy
- Reference grade
- Cost
- Free
- Effort
- A few minutes of reading
Every community water system in the US has to publish one each year, free, listing what it found and what the limits are. It is real laboratory data about the water leaving the plant and travelling the mains. What it cannot describe is your own plumbing.
Most systems publish hardness, often in both mg/L and grains per gallon, which is the unit a softener is sized and set in.
Where to find it: Your water bill, your supplier's website, or the EPA's index of reports. It is also called a Consumer Confidence Report or CCR.
Drop-count titration kit
- How trustworthy
- Dependable
- Cost
- Low cost
- Effort
- A few minutes, and it rewards being unhurried
Add reagent one drop at a time until the sample changes colour, and count the drops. The count is the answer, so there is no colour to judge by eye and no lighting to get wrong.
Add drops until the sample changes colour and count them. Sold for aquariums, for pools and by softener companies; all three are measuring the same thing.
Watch out: Kits report on different scales: mg/L as calcium carbonate, grains per gallon, or degrees. Check which one yours uses before comparing its answer with the band at the top of this page.
Where to find it: Pool shops and online, usually as part of a multi-test kit. Aquarium shops sell the same chemistry in smaller bottles.
Test strips
- How trustworthy
- Ballpark
- Cost
- Low cost
- Effort
- Under a minute, wherever you drew the sample
A plastic strip with reagent pads on it. Dip it, hold it level, and match each pad against the chart on the bottle at the time the label tells you to. Most strips read several parameters at once.
One pad, one dip, and enough of an answer to decide whether hardness is your problem at all.
Where to find it: Pool shops, hardware stores, supermarkets and online, sold both per parameter and as multi-packs. Buy strips made for your kind of water: pool strips and drinking water strips read very different scales for the same chemistry.
What you can see, taste and feel
- How trustworthy
- Ballpark
- Cost
- Free
- Effort
- None
Not a measurement, and it belongs here anyway: it is free, it is continuous, and it is what tells most people to test at all. Treat it as the prompt for a number, never as the number.
Scale in the kettle, a film on the shower screen, spots on dry glassware and soap that will not lather are all hardness. They tell you it is high; they will never tell you how high, and a softener is sized on a number.
Where to find it: A clean, clear glass and a sheet of white paper.
Certified laboratory, mail-in kit
- How trustworthy
- Reference grade
- Cost
- Most expensive
- Effort
- Careful sampling, then days or weeks of waiting
You are posted bottles and instructions, you fill them exactly as told, and you post them back. Weeks later a report arrives with figures nobody has to interpret by eye. This is what a result you intend to act on should be built from.
Included in any general panel, and it separates calcium from magnesium, which matters if you are treating the water rather than just describing it.
Where to find it: State-certified drinking water laboratories; your state's certification officer keeps the list, and many public health departments will point you at one.
Taking the sample
For several of these the sample is where the error is, and no instrument recovers from a bad one.
- • If you have a softener, take two samples: one from an outside tap or the line ahead of it, and one from the kitchen. The pair is the only way to know whether the unit is working, and it is the test to repeat when you suspect it has stopped.
- • Hardness does not change with standing time or time of day, so there is no trick to the sample itself.
Further reading: US EPA: Consumer Confidence Reports, the annual report every community water system publishes
If it is too low
Soft water. Soap lathers readily and rinses less easily, giving a slippery feel. Very soft water can be mildly corrosive to plumbing.
- • Nothing to do for health reasons.
- • If it is very soft and your pipes are copper, keep an eye on pH; soft, acidic water together are what corrode plumbing.
If it is too high
Scale builds up in kettles, heaters and coffee machines, soap lathers poorly, and glassware spots. Not a health concern.
- • A water softener is the standard whole-house answer.
- • For a targeted fix, a scale filter on the coffee machine or an inline filter at the boiler is far cheaper than treating the whole property.
- • Descale kettles and shower heads on a regular schedule.
Common questions
Is hard water bad for your health?
No. Hard water is not a health hazard, and the calcium and magnesium in it are dietary minerals. It is classed as an aesthetic and practical issue, not a health-based one. The case for treating it is about appliances, soap and comfort.
What hardness level causes limescale?
Scale becomes noticeable above roughly 120 mg/L and pronounced above 180 mg/L, especially anywhere water is heated. Kettles, water heaters and espresso machines show it first because heat drives calcium out of solution.
Does a water softener make water taste salty?
It should not. Ion-exchange softeners swap calcium and magnesium for a small amount of sodium, enough to be worth knowing about if you are on a strictly sodium-restricted diet, but normally well below a level you can taste.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.