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Urine in swimming pool

Have you ever worried about the secret tracer chemical in swimming pools, the one that turns bright red when you pee in the pool?

Have you ever worried about the Secret Tracer Chemical in swimming pools - the one that turns bright red when you pee in the pool? Orson Welles (the original voice of the “War of the Worlds” radio broadcast and the face of the “Citizen Kane” guy) reckoned that he had some of this chemical in his pool. According to him, only “the nicest, cleanest, most respectable people” would wee in the water. But there's no such chemical.

In nature, clean water pools seem to exist without any effort at all. But it takes a lot of science to replicate this, and have a swimming pool with water that is pleasant and free of germs. Professor Ben Selinger devotes a whole chapter to this in his book, Chemistry in the Marketplace . Chlorine is a cheap and very effective chemical to kill various nasties in your swimming pool. Once in the water, it immediately splits into hypochlorous acid (very quick at killing bacteria) and hypochlorite ions (very slow at killing bacteria). What the hypochlorite ions can do quickly is fade your swimming cossie, so you should rinse it immediately after leaving the pool.

Some of the Swimming Pool Science is exactly the opposite of what you would expect. For example, people often sniff the air at their local swimming pool, and then confidently proclaim, “There's too much chlorine in the water, I can smell it.” The truth is the exact opposite - there's not enough chlorine!

The chemistry runs like this. There's organic nitrogen in the water, which came from urine, sweat, dead insects, bacteria, etc. This organic nitrogen has used up all the chlorine in the hypochlorous acid and hypochlorite ions, and so there's no chlorine left. The chlorine and the nitrogen have combined together to make a class of chemicals called “chloramines” - which is what you are smelling. And the cure? Add more chlorine, and after a while, the smell goes away.

Now this sounds weird, so let me explain it. After all, how can it be that if you have a chlorine-like smell coming out of your pool, you can fix it by adding more chlorine?

You see, chlorine goes through a few chemical stages in destroying (or burning) the nasty organics. It firstly forms monochloramine, then dichloramine, then trichloramine and runs through a few more steps before ending up at nitrogen gas, or nitrates. Now it's the volatile trichloramine (in the middle of these chemical reactions) that has the supposed “chlorine” smell. If there's not enough chlorine, the reaction gets stuck at one of the chloramine stages. So when you add more chlorine, you push the reaction along out of the trichloramine stage - and the smell goes away.

So, is there a chemical that can be added to swimming pools, to change colour and mark out naughty people who wee in the water? According to Prof. Selinger, almost certainly not. Urine is made from water, inorganic salts, urea, creatinine, ammonia, catecholamines, allantoin and the breakdown products of red blood cells, which give it its yellowish colour. There are also many other chemicals in varying ratios, depending on your health and many other factors. Which one of these many chemicals will you choose to react with? If a chemical can react to urine, it might also react to your sweat. This is such a difficult problem, that it seems that nobody has tried to solve it.

And if such a chemical did really exist, surely cheeky kids would urinate while swimming past other kids, to put the blame onto them.

Maybe the only cure for the urine-pool problem is that used by the Preppy Pup Country Club in New Jersey . It's their very first day care centre catering exclusively for dogs. The rule is plainly posted, for all dogs to read, “Welcome to our ool. Notice that there's no P in it. Please keep it that way.”

Tags: biology, chemistry, pseudoscience, weird-and-wonderful

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Published 23 November 2006

© 2014 Karl S. Kruszelnicki Pty Ltd