Find a clean glass or plastic bottle with a tight-fitting cap. Fill the bottle 1/3 full with water straight from the faucet (should be about 8 to 10 ounces).
Add 10 drops of dishwashing liquid; use pure liquid soap (not "detergent") and shake well for at least 10 seconds. Set the bottle down and observe the results:
■ If the soapy solution foams up quickly, creating a lot of suds, and the water below the suds layer is relatively clear, you probably have at least fairly soft water.
■ If the solution does not foam up well, creating only a shallow layer of suds, and the water below the suds is cloudy, you likely have hard water.