What hardness actually is
Hard water carries dissolved calcium and magnesium picked up from rock and soil. Those minerals are generally not considered a health concern. They are a plumbing problem, because they come out of solution when water is heated and form scale.
That scale coats heating elements, clogs aerators and showerheads, and leaves white spots on glass. A tank water heater collects it at the bottom, and a tankless unit collects it inside the heat exchanger.
The scale plumbers and labs use
| Classification | Hardness in mg/L as calcium carbonate |
|---|---|
| Soft | 0 to 60 |
| Moderately hard | 61 to 120 |
| Hard | 121 to 180 |
| Very hard | More than 180 |
These are the USGS ranges. Some labs and equipment makers report in grains per gallon, which is a different unit, so check which one a report uses before comparing numbers.
Signs you can see
- White or chalky crust on faucets and showerheads.
- Spots on glasses and dishes after the dishwasher.
- A film on shower doors that does not wipe off easily.
- Soap that lathers poorly.
- A kettle or coffee maker that scales up quickly.
These signs say the water has hardness. They do not say how much. For that, you need a test.
How to test your own tap
Pick a tap
Use a cold tap that has not been run through a softener.
Use a test kit
Hardware stores sell test strips that give a rough reading. A lab test gives an exact number.
Read the result
Compare it with the scale above and note the units.
Check the supplier's report
Your water supplier publishes an annual report. It describes the source water. A tap test shows what reaches your house.
What a softener does
A softener swaps calcium and magnesium for sodium or potassium. That reduces scale buildup, which helps protect the water heater and fixtures and helps soap work. It does not make water safer to drink and it does not remove lead.
See water softener installation for what the install involves, and water filtration for removing specific contaminants. They solve different problems.
Hard water and your pipes, fixtures and appliances
Scale does not stay where it forms. In a pipe, it narrows the opening over years, and a line with scale carries less water at a lower pressure. In a showerhead, it clogs the holes and gives an uneven spray. In a dishwasher, it leaves spots and can shorten the life of the heating element.
Faucet aerators are the easiest place to see it. Unscrew the tip and look for white crust. Soaking it in vinegar dissolves the scale and often restores the flow.
Cleaning scale without damaging anything
Showerheads
Remove and soak in white vinegar for several hours, then rinse. Check the manufacturer's instructions for finishes that vinegar can mark.
Aerators
Unscrew, soak and brush the screen.
Kettles and coffee makers
Run a vinegar and water cycle, then rinse thoroughly.
Water heaters
Flush the tank once a year. A plumber can show you how, or do it.
Cleaning treats the symptom. If scale returns quickly, the water has high hardness, and a softener may be the long-term answer.
Soft water is not always the answer
A softener adds cost, uses salt or potassium and needs maintenance. In water that is only moderately hard, regular cleaning and a yearly tank flush may be enough. In very hard water, a softener protects equipment that costs much more than the softener.
Make the decision with a test result in hand. Compare the number with the scale above and think about what you own. A new tankless heater is much more sensitive to scale than an old tank, and that changes the math.
What to ask when you call about hard water
- What did the test strip or lab report say, and in which units?
- How many people live in the house?
- What water heater do you have and how old is it?
- Is there a drain and an outlet near the water main?
- Do you or anyone in the house restrict sodium?
These answers let a plumber size a softener sensibly, or tell you that you do not need one. A plumber who sells you equipment without asking about your water test is skipping the most important step.
Converting a lab report
Some labs report hardness in grains per gallon instead of milligrams per liter. One grain per gallon equals about 17.1 mg/L, so a report of 7 grains per gallon is about 120 mg/L, the top of the USGS moderately hard range.
Check the unit printed on the report before comparing it with the scale above. A number that looks small in grains can be a hard reading in milligrams per liter.
Water heaters and hard water
Scale in a tank water heater insulates the burner or the element from the water. The heater works harder to do the same job, and the bottom of the tank can overheat. Flushing the tank once a year removes sediment and extends its life.
For tankless units, descaling is part of normal maintenance. A unit that is never descaled in hard water can lose output or fail early. See tankless water heaters for more.