Grab a clear, empty water bottle. Fill it about halfway with tap water from your kitchen sink.
Now, add exactly five drops of plain liquid dish soap. No, not the fancy moisturizing kind—just some basic, run-of-the-mill soap.
Screw the cap on tight and shake it like a Polaroid picture. Watch what happens. If you see a mountain of fluffy suds, you’re probably in the clear. If you get a sad, cloudy puddle with barely a whisper of bubbles? That’s hard water waving hello.
