You can establish which side of the line your water sits on in a few minutes with nothing bought, because hardness advertises itself in several places once you know where to look. Getting the exact figure takes a test, but deciding whether you have a problem worth measuring does not need one.
Four places to look right now
Unscrew the kitchen tap aerator and look at it: chalky white deposit means hard, and how much has built up says how hard. Look inside the kettle for the same crust. Look at the shower screen and taps for a film that returns within days of cleaning. And notice the soap, since hard water gives poor lather, leaves a scum ring in the bath and leaves skin feeling tight after washing, while soft water lathers generously and rinses to a slippery feel.
The bottle test
Part fill a clear bottle with cold tap water, add a few drops of pure liquid soap rather than detergent, cap it and shake hard. Soft water gives a thick head of lather that persists, with clear water beneath. Hard water gives very little lather, it collapses quickly, and the water below turns cloudy with soap scum. The more soap it takes to raise a lasting lather, the harder the water. It costs nothing and separates the two ends of the scale reliably.
Getting the actual number
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, and which band you are in decides whether treatment pays and what capacity it needs. On a municipal supply the annual water quality report often carries the figure at no cost. Otherwise a titration kit or hardness strips give it in minutes. Softener settings are usually entered in grains per gallon, so expect to convert.
The instrument that will mislead you
A TDS pen measures conductivity from every dissolved ion, so it cannot isolate calcium and magnesium and two supplies with identical readings can differ completely in hardness. It is also why softened water reads much as it did untreated: sodium replaced the calcium ion for ion. If you already have a softener and want to know it is working, test before and after it with a hardness kit rather than a pen. Our soft water guide covers what treatment changes.
Questions people ask about how to tell if water is hard or soft
What is the quickest sign of hard water?
Chalky white deposit on the tap aerator and inside the kettle, and a film on the shower screen that returns within days.
How does the soap bottle test work?
Shake cold tap water with a few drops of pure liquid soap. A thick persisting lather means soft; little lather and cloudy water means hard.
Where do I get the actual figure free?
On a municipal supply, the annual water quality report often lists it. Otherwise a titration kit or strips take minutes.
Why does soft water feel slippery?
Soap rinses away completely and skin oils are not stripped by reaction with minerals. It is the absence of residue, not the presence.