- "Take a clean empty plastic bottle having a cap (such as a clean, clear pop bottle);
- Remove the cap;
- Open your tap water faucet and fill the bottle with about a half-cup of water (8 to 10 ounces);
- Add 10 drops of dish washing liquid;
- Shake well;
- If the soapy solution foams up quickly you are good and the water is not hard;
- If it does not foam up but instead creates a milk-curd-like or soapy film on the water surface then the water is likely hard."
I believe this works if your water is really hard. Our water is somewhere in the middle between extremely hard and soft, and as i tried that experiment, the dish washing soap foamed, but not as much as one would expect it to foam.
I hope this was helpful!