Science reveals the truth about pee in pools

Child in swimming pool

For germ-fearing people, swimming pools can be a nightmare. It's understandable, given that an active swimmer can sweat up to a litre in a warm pool over an hour. 

There's also the major issue of peeing, but there's never been an easy way to measure the amount of urine in a swimming pool, until now.

Scientists in Canada have developed a test to tell how much pee is in a pool, by measuring the concentration of acesulfame potassium - an artificial sweetener commonly in processed food, the Guardian has reported.

The sweetener passes through the body unaltered, and is easy to detect in the water. The researchers took samples from 31 actively used pools and hot tubs in two Canadian cities, and more than 90 samples of clean tap water.

  • The concentration of the sweetener in the pools and hot tubs ranged from 30-7110 nanograms per litre of water - up to 570 times more than the levels found in the tap water samples.
  • The study estimated swimmers released more than 7 gallons (26.5 litres) of urine in a 110,000-gallon (about 416,400-litre) pool in one instance.

The scientists' findings appeared in the American Chemical Society's Environmental Science & Technology Letters journal.

Pee and pools facts:

  • The New Zealand Standard - Pool Water Quality says: "Pollution of pool water by pool users through excretion is common. A pool user can lose up to one litre of sweat per hour when actively swimming in water at 24degC at an ambient air temperature of 30degC.
  • The standard says a normal adult excretes about 25-50ml of urine per pool session. "The contribution from this source can be lessened if the bladder is emptied before entering the pool," it says.
  • There's been a widely-known urban myth that some pools have a urine-detecting chemical that changes the colour of the water when urine mixes with it. While this could be an effective way to scare a young one from peeing, it is not true.

At the London 2012 Olympics, US swimmer Michael Phelps admitted to peeing in the pool.

"I think everybody pees in the pool," he said.

"Chlorine kills it, so it's not bad."

Auckland's Olympic Pools manager John Nixon says they spend a lot of time - and about $120,000 a year - constantly refilling the pools with fresh water.

The pools get tested up to eight times per day, and the water is kept clean with chlorine gas, which is 100 percent pure chlorine, he says.

They also get Watercare to test the pools at random.

"We've got 1.4 million litres of water. It takes a lot of wees to have any effect. And everyone that comes in and goes out of the pool is taking water with them, so we're constantly replenishing with fresh water."

On top of that, Auckland is blessed with good quality water, and swimmers are good as far as staff are aware, Mr Nixon says.

They also use a filtration system that removes particles down to half a micron. In comparison, a strand of hair is about 100-120 microns thick.