Guide
How to test water hardness at home
Four ways, from a free lookup to a drop-count kit.
Short answer
Dip a hardness test strip in cold tap water for a second and match the pad to the colour chart: that gives a reading in ppm or gpg within one colour band. For a number accurate enough to size a softener, use a drop-count titration kit, where each drop usually equals 1 gpg. Your water utility’s annual report and the ZIP lookup give the figure without testing at all.
The four ways to find your hardness
- Look it up. Public water systems publish hardness in their annual Consumer Confidence Report. The ZIP lookup gives the county figure from public monitoring data.
- Test strips. Quick and cheap. Run the cold tap for a few seconds, dip the strip for about a second, wait the time on the packet and compare colours.
- Drop-count titration kit. Add reagent drops to a measured sample until it changes colour and count the drops. The most accurate home method.
- Soap test. Shake a few drops of pure liquid soap in a bottle of tap water. Little lather and a cloudy look mean hard water. It tells you whether, not how much.
Reading a test strip
| Pad (ppm) | Grains per gallon | Classification |
|---|---|---|
| 0 | 0.0 | Soft |
| 25 | 1.5 | Soft |
| 50 | 2.9 | Soft |
| 120 | 7.0 | Moderately hard |
| 250 | 14.6 | Very hard |
| 425 | 24.8 | Very hard |
ppm on a strip means mg/L as calcium carbonate; divide by 17.118 for grains per gallon. The hardness converter does any unit.
Are test strips accurate?
Accurate enough to classify your water, not to measure it. A strip reads in steps, and the gap between two pads can be wide: between the 120 and 250 ppm pads lies 7.6 gpg, which is the difference between moderately hard and very hard. If your result falls between pads, or you are sizing a softener, use a drop-count kit. Strips do expire and are ruined by damp, so check the date and keep the lid tight.
Test hot or cold?
Cold, from a tap that does not pass through a softener or filter, after running it for a few seconds. Hot water that has sat in a heater can read lower, because some of the hardness has already dropped out as scale.