Grab a clean, clear plastic bottle with a tight lid. Fill it about one-third full with tap water, then add five drops of pure liquid dish soap—not detergent, just basic soap.
Secure the lid and shake vigorously for about ten seconds. Now, watch what happens. If the water turns cloudy and the foam disappears quickly, you’ve got hard water.
Soft water, on the other hand, will produce a thick, fluffy layer of suds that sits on top like a cloud. It’s almost too easy—but science confirms this test works because soap reacts with calcium to form soap scum.
