Fill a clear jar halfway with tap water, then add a few drops of pure liquid soap (no detergents or additives). Shake it vigorously for ten seconds. If the water turns milky with voluminous suds, you’ve got soft water. If the suds are thin, flat, and the water looks cloudy instead of foamy—bingo, hard water.
A fun little cultural tangent: in ancient Rome, people used hard water from the Tiber River to wash clothes, and they had to rely on urine as a degreaser. Consider your modern soap a luxury upgrade, even if it doesn’t lather like a shampoo commercial.
The "Tea Film" Aesthetic
Brew a cup of black tea and let it sit for a few minutes. Look at the surface for a thin, iridescent film—like an oil slick in miniature. That’s the tannins in the tea reacting with the calcium in your water. It’s perfectly safe, but it does make your morning cuppa look a bit like a science experiment.
Hard water also dulls the flavor of tea and coffee. The minerals bind to the compounds that give your drink its taste, leaving you with a flatter, more bitter brew. The Brits, masters of tea, have long fought this battle with water softeners and kettles full of limescale.
