Pour a little dish soap into a clear jar of tap water, put the lid on, and shake it like you’re at a rock concert. If the water turns cloudy and produces almost no suds, it’s hard. Soft water will erupt into a frothy, fluffy cloud of bubbles like a cappuccino gone wild.
Do not be fooled by a tiny suds layer—if it vanishes in ten seconds, you’ve got Mount Mineral in your glass. This works because those calcium ions bind to the soap before it can bubble, stealing your suds like a thief in the night.
