Unsolved:Urine-indicator dye

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Short description: Urban legend

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.[1][2] A 2015 report from the National Swimming Pool Foundation called this "the most common pool myth of all time", with nearly half of Americans surveyed by researchers believing that the dye existed.[3]

Urine is difficult to detect, as many of the naturally occurring compounds within urine are unstable (i.e., short-lived, quickly disappearing) and react freely with common disinfectants, such as chlorine, creating a large number of disinfection by-product (DBP) compounds from the original organic chemicals in urine.[4][5].

An accurate urine test would require testing for urine's chemical profile in addition to (or even instead of) its byproducts produced by typical pool chemicals. However, testing for the presence and/or concentration of the byproducts, which can be created from several non-urine urea-containing sources such as sweat[6], would lead to many false positives, indicating that urine has been detected even if no urine was actually present, with significantly higher false positive rates in the case of people with uremic frost from impaired kidney function.[6]

  • In other words, it may appear that a dehydrated sweaty person or a person with a medical condition would be peeing in the pool with this theoretical pee-detector chemical, despite them not actually peeing.


Rumours of the origin of urine indicator-dye go back at least as far as 1958,[1] and the story is commonly told to children by parents who do not want them to urinate in the pool.[3] A 1985 biography of Orson Welles describes him using such a dye as part of a prank in 1937.[1][7]

In the film Grown Ups this myth was portrayed as fact for comedic effect.[8]

Further Reading


References

  1. ↑ 1.0 1.1 1.2 Mikkelson, Barbara (December 14, 2000). "Piscine of the Crime". Snopes. http://www.snopes.com/science/poolpiss.asp. 
  2. ↑ Hannah Devlin (1 March 2017). "How much pee is in our swimming pools? New urine test reveals the truth". The Guardian. https://www.theguardian.com/science/2017/mar/01/how-much-pee-is-in-our-swimming-pools-new-urine-test-reveals-the-truth. 
  3. ↑ 3.0 3.1 O'Neil, Lauren (25 June 2015). "Pee, not chlorine, causes red eyes from swimming pools: CDC". CBC News. http://www.cbc.ca/news/trending/pee-chlorine-red-eyes-swimming-pools-cdc-1.3127865. 
  4. ↑ Lindsay K. Jmaiff Blackstock (1 March 2017). "Sweetened Swimming Pools and Hot Tubs". Environmental Science & Technology Letters 4 (4): 149–153. doi:10.1021/acs.estlett.7b00043. Bibcode: 2017EnSTL...4..149J. 
  5. ↑ Dr Karl Kruszelnicki (2010). Curious and Curiouser. Pan Macmillan. pp. 203–207. ISBN 9781742624266. https://books.google.com/books?id=RwrscJRxs0sC&pg=PA203. 
  6. ↑ 6.0 6.1 "Why Your Sweat Contains Urea and What It Means" (in en). Biology Insights. July 24, 2025. https://biologyinsights.com/why-your-sweat-contains-urea-and-what-it-means/. 
  7. ↑ Sally Magnusson (2011). Life of Pee; The Story of How Urine Got Everywhere. Aurum Press. p. 143. ISBN 9781845138011. https://books.google.com/books?id=Taz0AgAAQBAJ&pg=PT143. 
  8. ↑ Zimmerman, Edith (2010-06-14). "The Swimming Pool Chemical That Turns Pee Blue in Grown Ups Is a Myth, Right?" (in en). https://www.vulture.com/2010/06/is_there_actually_a_swimming_p.html. 



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