Urine-indicator dye is a mythical substance that is supposed to be able to react with urine to form a colored cloud in a swimming pool or hot tub, thus indicating the location of people who are urinating while they are in the water. A 2015 report from the

National Swimming Pool Foundation The National Swimming Pool Foundation (NSPF) was a United States 501(c)(3) non-profit organization, most known for selling the Certified Pool Operator certification, amongst many other less known products. The Certified Pool Operator certificati ...

called this "the most common pool myth of all time", with nearly half of Americans surveyed by researchers believing that the dye existed. Urine is difficult to detect, as many of the naturally occurring compounds within urine are unstable and react freely with common disinfectants, such as chlorine, creating a large number of

disinfection by-product Disinfection by-products (DBPs) result from chemical reactions between organic and inorganic matter in water with chemical treatment agents during the water disinfection process. Chlorination disinfection byproducts Chlorinated disinfection agen ...

(DBP) compounds from the original organic chemicals in urine. In an article published in 2000, Snopes confirmed such a dye did not exist. Rumours of the origin of urine indicator-dye go back at least as far as 1958, and the story is commonly told to children by parents who do not wish them to urinate in the pool. A 1985 biography of

Orson Welles George Orson Welles (May 6, 1915 – October 10, 1985) was an American actor, director, producer, and screenwriter, known for his innovative work in film, radio and theatre. He is considered to be among the greatest and most influential f ...

describes him using such a dye as part of a prank in 1937.

References

{{Urban legends Fictional materials Swimming pools Urban legends Urine