The pungent smell of chlorine at your local swimming pool may reassure you that the chemicals used to kill germs and bacteria are working.
You may even find the smell ‘nostalgic’ and be transported back to hot 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 labelled ‘the most terrifying experiment’ he’d ever conducted, Mr Rober, 44, compared the odour of two buckets of chlorine-containing water.
The only difference between the two is that one contained a drop of pee.
Former NASA and Apple engineer Mark Rober has confirmed the stomach-churning truth why swimming pools stink in what he has called ‘the most terrifying experiment’ he has ever done
To be able to compare the stench between chlorinated water and chlorinated water that contains urine, he added a drop of pee to bucket B
In the viral Instagram video, which 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, to be able to compare the stench between chlorinated water and chlorinated water that contains urine, he added a drop of pee to bucket B.
A lid went on both of the buckets and they were left for 24 hours to fester.
After a day was up it was time to put the buckets of water to the smell test.
Mr Rober smelt bucket A, which only contained water and chlorine and confessed that it didn’t ‘smell like anything’.
‘That smells just like water even though there is four times the recommended concertation of chlorine for this volume,’ he said.
But he added that the lack of chlorine smell made him ‘nervous’ to test bucket B.
In the video Mr Rober can be seen sniffing the second bucket of chlorinated water, which he admitted had that ‘nostalgic’ swimming pool stench.
‘This smells like a pool even though the only difference between these two is that this has a little bit of pee in it,’ he said.
‘This is a nostalgic smell. This smells like summers and vacations at hotels with pools and water parks. Turns out it was just pee,’ he added.
The experiment confirmed Mr Rober’s suspicions that urine and sweat cause the chemical change in chlorine to produce that well-known swimming pool smell
So, why does sweat and urine give chorine a strong smell?
Chlorine when added to water releases two chemicals that help kill waterborne germs, 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 in to contact with sweat, oils and urine it is reduced to form chloramines, according to the American Chemistry Council.
These chloramines are formed in 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 ammonia’s hydrogen ions is replaced with chlorine, monochloramine is formed.
And replacing one more hydrogen ion with chlorine produces dichloramine, if you replace all three of ammonia’s hydrogen ions with chlorine, it forms trichloramine, also known as nitrogen trichloride.
It is trichloramine that’s responsible for the swimming pool stench.
But simple things such as showering to wash off sweat before getting into a swimming pool can help to minimise the formations of these chloramines and therefore reduce the pong.
