If you pee in the pool, it’ll go blue! There’s a special dye in there, designed to detect urine, and it’ll billow around you in a big, embarrassing, pissy cloud, and everyone will know you’ve done it, and you’ll be hounded out of town as a known pool-piddler. Everybody knows that, right? Except it isn’t true. It doesn’t even stand up to any scrutiny as an idea — what chemical specifically detects wee-wee? Would something that would react that dramatically to a dribble of micturition be safe to swim in? And if it happened, and someone was suddenly surrounded by...