Stomach-churning Truth About the Chlorine Smell in Swimming Pools (Yes, the Rumor is True)

The pungent smell of chlorine in your local pool can reassure you that the chemicals used to kill germs and bacteria are working.

You may even find the scent ‘nostalgic’ and take you back to warm summer days, water parks and even hotel pools.

But former NASA and Apple engineer Mark Rober has confirmed the stomach-churning reason swimming pools smell so strongly.

In what he called “the most terrifying experiment” he had ever conducted, Mr Rober, 44, compared the smell of two buckets of chlorinated water.

The only difference between the two is that one had a drop of pee in it.

To compare the stench between chlorinated water and chlorinated water containing urine, he put a drop of urine in bucket B

In the viral Instagram videowhich has amassed 778,000 likes, Mr Rober filled two identical buckets, one labeled A and the other B with ‘pure’ water.

He then added four times the recommended concentration of chlorine for that volume of water to both buckets.

However, in order to compare the stench between chlorinated water and chlorinated water containing urine, he put a drop of urine in bucket B.

A lid went on both buckets and they were left to fester for 24 hours.

After a day had passed, it was time to put the buckets of water to the smell test.

Mr. Rober smelled bucket A, which contained only water and chlorine, and admitted that it “didn’t smell like anything.”

“That smells just like water, even though there is four times the recommended amount of chlorine for this volume,” he said.

But he added that the lack of chlorine smell made him “nervous” about testing Bucket B.

In the video, Mr Rober can be seen sniffing the second bucket of chlorinated water, which he admitted had that “nostalgic” pool stench.

“This smells like pee, even though the only difference between the two is that there’s a little bit of urine in them,” he said.

‘This is a nostalgic scent. This smells like summers and holidays in hotels with swimming pools and water parks. Turns out it was just pee,” he added.

The experiment confirmed Rober’s suspicion that urine and sweat cause the chemical change in chlorine to cause the familiar swimming pool odor.

Why do sweat and urine give chorine a strong odor?

When chlorine is added to water, it releases two chemicals that help kill germs in the water, one is called hypochlorous acid and the other is called hypochlorite ion.

Together these chemicals are known as ‘free available chlorine’ and when it comes into contact with sweat, oil and urine it is reduced to chloramines, according to the American Chemical Council.

These chloramines are formed in swimming pool water by the reaction of hypochlorous acid with ammonia, a component of sweat and urine.

When hypochlorous acid reacts with ammonia, three reactions can occur, each involving the replacement of hydrogen ions with chlorine ions. When one of the hydrogen ions of ammonia is replaced by chlorine, monochloramine is formed.

And if you replace another hydrogen ion with chlorine, dichloramine is created. If you replace all three hydrogen ions of ammonia with chlorine, dichloramine is formed. trichloramine, also known as nitrogen trichloride.

It is trichloramine which is responsible for the pool stench.

But simple things like showering to rinse off sweat before getting in a pool can help minimize the formation of these chloramines and therefore reduce pong.