Use a **water hardness test kit**, available from hardware stores, aquarium shops, or water-treatment suppliers. A **drop-count titration kit** gives a more precise reading than test strips and is useful for checking a softener.

To check yours:

1. Take a sample from a cold-water tap supplied by the softener. Run the tap briefly first to clear standing water.
2. Test it according to the kit’s instructions.
3. Compare it with water taken before the softener or from a tap you know bypasses it. Outdoor taps sometimes do.

Hardness is usually reported as **ppm (mg/L) as calcium carbonate** or **grains per gallon**. One grain per US gallon equals about **17.1 ppm**.

| Hardness, ppm | Classification |
|---|---|
| 0–60 | Soft |
| 61–120 | Moderately hard |
| 121–180 | Hard |
| Over 180 | Very hard |

A working ion-exchange softener should produce water with very little measurable hardness. If the softened sample is nearly as hard as the untreated sample, check the salt supply, bypass valve, and regeneration settings.

A **TDS meter won’t tell you the hardness**: it measures dissolved substances generally, and a softener exchanges calcium and magnesium for sodium or potassium rather than removing all dissolved minerals. Existing calcium deposits also won’t disappear just because the softener is working again.