Before buying any test or any equipment, it is worth knowing that the answer may already exist somewhere, and that the free checks are good enough to decide whether a paid test is warranted. Hardness is one of the few water problems you can diagnose from the evidence around the house in a few minutes.
The evidence around you
The kettle is the honest witness: a white crust inside means hardness and the speed it returns after descaling tells you roughly how much. The kitchen tap aerator, unscrewed and looked at, shows years of accumulation in a form you can hold. The shower screen and taps show a film that returns within days of cleaning. And the soap tells you plainly: hard water gives poor lather, a scum ring in the bath and a tight feeling on skin after washing.
Where the figure may already be written
On a municipal supply the annual water quality report often lists hardness, which makes the number free and laboratory accurate, and every community water system publishes one. The second place is your neighbours and any local plumber, since hardness is a regional property of the water source rather than something that varies house to house on the same mains. If a softener is common on your street, that is a data point worth taking seriously.
Putting a band on it
The USGS classes water as soft at 0 to 60 mg/L as calcium carbonate, moderately hard at 61 to 120, hard at 121 to 180 and very hard above 180 mg/L. That banding is what decides whether treatment pays and what capacity it needs, and it is worth getting right because the difference between the top of moderately hard and the middle of hard changes the answer. Hardness strips or a titration kit give it in minutes for very little.
One instrument to avoid for this
A TDS pen measures conductivity from every dissolved ion and cannot isolate calcium and magnesium, so two supplies reading identically can differ completely in hardness. It also reads much the same before and after a softener, since sodium replaced the calcium ion for ion, which regularly convinces owners a working unit has failed. Use hardness specific chemistry for this question. Our hard water shower head guide covers what treatment changes at the fixture.
Questions people ask about how to know if your water is hard
Can I tell without buying a test?
Usually. Crust in the kettle, deposit on the tap aerator, film on the shower screen and poor lather together give a confident answer.
Where might the figure already be recorded?
The annual water quality report on a municipal supply often lists hardness, which makes the number free and accurate.
What are the hardness bands?
Soft at 0 to 60 mg/L as calcium carbonate, moderately hard 61 to 120, hard 121 to 180 and very hard above 180 mg/L.
Why not use a TDS pen?
It responds to all dissolved ions and cannot isolate calcium and magnesium, and it reads the same before and after softening.