Checking hardness takes a few minutes and settles an expensive question. Hardness is dissolved calcium and magnesium, it is what forms scale and blocks soap from lathering, and it is measured either in grains per gallon or as milligrams per liter of calcium carbonate. A drop titration kit gives a number precise enough to size a softener from.
Take the sample from the right place
Use a cold tap and let it run until the water feels genuinely cold, so you are measuring supply water rather than water that has been standing in the pipes. Do not sample from a hot tap, a filtered faucet or a refrigerator dispenser. If a softener is already installed, find the raw supply: an outside hose bib is often plumbed ahead of it, or the softener's own bypass can be used. Rinse the sample container with the water you are about to test before filling it.
Run the test and read it honestly
A drop titration kit asks you to measure a set volume of water, add reagent one drop at a time, and count the drops until the color changes. Cap and shake between drops, count carefully, and repeat the test once to confirm. Strips are quicker but place you in a wide band with a subjective color match, and strips from a tub that has been open in a humid bathroom drift. Whichever tool you use, write down the number and the unit, because the unit is easy to lose track of later.
Read the number against the standard bands
The USGS classification is the common reference: soft water is 0 to 60 mg/L as calcium carbonate, moderately hard is 61 to 120, hard is 121 to 180, and very hard is above 180 mg/L. If your kit reports grains per gallon, convert before comparing. Households in the soft and moderately hard bands rarely need a softener. Hard water usually justifies one on appliance protection alone, and very hard water makes scale a continuous maintenance problem in heaters, valves and fixtures.
Cross check with what you already have
Community water customers can look up their utility's annual Consumer Confidence Report, which the EPA maintains a finder for, and it often lists an average hardness for the system. That is a useful sanity check against your own test, though your tap is the figure a softener has to be sized from. Well owners have no such report and should fold hardness into a broader panel that also covers iron, manganese, pH, nitrate and bacteria, because those change the equipment specification.
What to do with the number
Softener sizing is calculated from measured hardness, household size and any iron present, which together set how much capacity is consumed between regenerations. Give your installer the measured figure rather than a guess, and keep the test result so a metered valve can be programmed correctly at commissioning. If you are on a well, retest after seasonal shifts, since water chemistry moves with rainfall. Our local water hardness testing guide covers arranging a professional test when the decision is large.
Questions people ask about check water hardness
What is considered hard water?
Using the USGS bands, water in the 121 to 180 range as calcium carbonate counts as hard, and anything above that band as very hard.
Can I check hardness without a kit?
Only roughly. Shaking soap in a bottle of water and watching the lather is an old trick, but it gives no number you can size equipment from.
Should I test hot or cold water?
Cold, and let it run first. Hot water has passed through the heater, where scale has already formed and changed the chemistry.
How often should I retest?
City supplies are stable enough that one test is usually sufficient. Wells should be retested after seasonal changes, since chemistry shifts with rainfall.