Why Is Chlorine Used in Pools & Is It Still Necessary?

Swimming pools have been part of human society for thousands of years, and it’s fair to think that perhaps by this point we’ve tamed the need to dump eye- and nose-irritating chlorine compounds into our pools to stave off disease and infections. But while there have been some alternative (but similar) methods developed, the nature of life on earth demands that a large, relatively still body of water is going to need chemical treatment to make it safe for humans to swim through, submerge themselves in, or splash around day-in and day-out, often through a long, hot summer of use and exposure to - well - everything under the sun. 

Every pool of water in nature has chemicals in it, remember.

But the idea of a pool with no chemicals in it is romantic and attractive. Never mind that such an enclosure is a guaranteed breathing ground for bacteria, viruses, and parasites. When people think of chemicals they think of “bad chemicals,” and this shouldn’t necessarily be the case, as chemicals are the building blocks of all life on earth.

The benefit of chlorine treatment for pools (as well as spas and hot tubs) is because of its power as a disinfectant. It works like warfare on bacteria and viruses, taking them apart on the cellular level. If you think it stings your eyes, you ought to see what it does to a potentially harmful microorganism.

An important side benefit of that chlorination process is that it keeps the pool water clear of algae, dirt, and other detritus that can make a pool less than appetizing to leap into. And while you wouldn’t want to drink a glass of it, chlorinated pool water is safe for the exposure one gets while swimming laps.

If it’s the taste and the other mild unpleasant side effects of chlorination, there are other methods (still involving chlorine on some level) that can reduce those elements of your pool experience.

1. Ozone  - In these systems, ozone gas - even stronger as an oxidizer than chlorine -  is injected into water to stave off decontaminants. That said, toxic ozone can only treat water in pipes and not in the pool proper, so the process can take weeks to complete (as opposed to the relatively short time it takes to chlorinate a pool.)
2. Ultraviolet - In this method, it’s powerful (and power-bill elevating) UV light that eradicates microorganisms. But they’re tricky to use properly, as the oil in the pool water can interfere with the sleeves that protect the UV lamps. And, ironically, you’ll need to supplement the process with extra chlorine since the UV process breaks down chlorine.
3. AOP - New on the block as far as alternative systems of disinfecting a pool, AOP systems work by generating short-lived oxidizers called hydroxyl radicals that can eliminate contaminants, pathogens, and microorganisms. AOP systems are the most environmentally-friendly of these methods, but they do require a pump that runs 24 hours a day.

At the end of the day, whether you employ one of these systems to lower the chlorine afterburn in your pool or not, chlorine is still the best, safest, and most recommended way to disinfect a swimming pool. Even saltwater pools use chlorine.

So what’s with that chemical smell? Actually, it shouldn’t be there. A healthily-maintained pool should have no odor at all. That scent one associates with chlorine is actually from chemical compounds called chloramines, a kind of detritus that builds up in improperly treated pools when the chlorine combines with the bodily fluids that a swimmer leaves behind.

The cure for this is… more chlorine, in fact. Chlorine “shock treatment” is an essential part of proper pool maintenance, as superchlorination will take apart the organic compounds and ammonia that are building blocks for the pesky chloramines.

So chlorine is seemingly here to stay, but with proper maintenance and perhaps the addition or substitution of one of the alternative methods described above, there should be no nostril-burning chemicals or weird smells involved - leaving just a crystal-clear pool that invites the swimmer to dive in.