This is the easiest and most satisfying method, like using a lightsaber to cut a sandwich. You buy a little handheld device called a TDS meter (they’re cheap—like ten or fifteen bucks on the internet). It looks like a weird thermometer from a sci-fi movie. You just dip it in a glass of water, press a button, and—beep!—it gives you a number in parts per million (ppm).
The number is your TDS level. If it reads 50 ppm, you have almost no solids—basically melted rain. If it reads 500 ppm, you’ve got a lot of mineral action going on, like a tiny rock concert in your glass. A reading over 1,000 ppm? That water is thicc, my friend, and you might want to check for a weird taste or white residue on your kettle.
Pro tip: Don’t test your fish tank with the same meter you used for your coffee. Unless you want your goldfish to judge you. Rinse it well between uses, or you’ll be measuring guppy leftovers instead of dissolved solids.
