The Stronger Your Pool Smells Of Chlorine, The Dirtier It Really Is

The Stronger Your Pool Smells Of Chlorine, The Dirtier It Really Is - The potent smell of chlorine in a swimming pool is not exactly pleasant – but at least it means the pool is clean, right?

On the contrary – chlorine by itself is, in fact, odourless.

The smell comes from its reaction with urine and other bodily fluids – so the stronger the smell, the dirtier the water.

“If there’s a strong smell of chlorine, it means a lot of urea has got into the water,” explains Alexander Kaempfe, who heads the swimming and bathing pool water division of Germany’s Federal Environment Agency (UBA).

Urea enters the water through people’s urine, sweat and skin.

The reaction of chlorine with urea creates a chemical called trichloramine, and it’s this that is responsible for that pungent “swimming pool smell.”

The more urea in the water, the more trichloramine is formed.

Chlorine is used in pools to kill harmful bacteria and algae.

It also oxidises – chemically destroys – other materials such as dirt.

The standard concentration is between 0.3 and 0.6mg per litre of water.

The proper concentration of chlorine depends on numerous factors, points out Joerg Rosbach, a German technician and swimming pool operator.

The factors include what the water quality is, how many swimmers use the pool, how powerful is the water treatment system and if the sun shining.

Much of the urea in pool water comes from urine: from small children who pee in the pool, elderly people who can’t hold their urine and bathers who are simply too lazy to go to the toilet.

Even healthy bladders shed a few drops, Rosbach says. And then there’s the urea from sweat and people’s skin.

“If you pee in the pool, you introduce about 6g of urea,” Kaempfe says.

“That’s the amount given off by the skin of nearly 40 bathers.”

The UBA has calculated that every bather creates 0.16g of urea in pool water, on average.

How can urea contamination be reduced?

The most important way is for people to shower before entering the pool.

“Thoroughly showering removes 75 to 97 per cent of the urea on the skin,” the UBA points out in an information leaflet for public swimming pools.

Since not all bathers behave as they should, swimming pool operators have to remove considerable amounts of urea.

“The more people at the pool, the greater the bioload,” Rosbach says.

Canadian researchers have calculated that a 400,000-litre swimming pool typically contains 26.5 litres of urine.

In 2014, US scientists developed a novel way to detect urine in water.

When zinc ions are added, water containing urobilin – a by-product of urine – will give off a greenish glow under ultraviolet light.

The method was “hotly debated,” according to Kaempfe, who says a decision was taken not to use it in public pools for ethical reasons – so as not to discriminate against people who are incontinent, for example.

Is the stinky combination of chlorine and urea merely unpleasant, or also harmful?

“That depends on the concentration and on how sensitive the person is,” says Hermann Josepf Kahl, a spokesman for the Cologne-based Professional Association of Paediatricians.

He says trichloramine may cause respiratory problems, which can be dangerous for asthma sufferers.

It can also irritate the eyes, as well as the mucous membranes in the nose and throat.

“Chlorine is fine. The risks would be greater without it,” Kahl says, pointing out that swimming goggles can help prevent red eyes, and irritation to mucous membranes is usually temporary.

Rosbach, for his part, says he would “unhesitatingly” swim in just about any public pool.

Water treatment systems nowadays are very efficient, he notes, adding that people who go to a public pool can easily tell whether the operator is meeting its clean-water obligations.

“If you can already smell the pool at the entrance, then something’s amiss.”