The saltwater pool at the Residence Inn Washington, DC/Capitol

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Residence Inn Washington, DC/Capitol

Hot hotels — and even a lot of not-so-hot hotels — all seem to have a saltwater pool these days. (Want some examples? Click here, here, here, here, here, here, and here.) To the layman, a saltwater pool sure sounds like something special. I did an informal survey and found that most people assume that these exotic-sounding vessels are safer, healthier and/or more environmentally friendly than conventional swimming pools. Many figure the saltwater eliminates the need for chlorine, and some think it comes from the ocean itself — never mind that the nearest natural body of seawater may be hundreds of miles away. And some hotels encourage these ideas by making explicit claims to that effect in their marketing literature.

As you might have guessed by now, almost none of that’s true.

Conventional pools are treated with chlorine, usually in a liquid form, as a safe and effective way to sanitize the water of bacteria and viruses; to remove organic matter that people bring in (like sweat); and to prevent algae growth. Saltwater pools, it turns out, simply generate their own chlorine from salt, aka sodium chloride, or NaCl . They’re called saltwater pools because the water gets a little salty in the process.

Saltwater pools do have some advantages. Salt is generally safer to store and transport than liquid chlorine. More significantly, many people say the water in a saltwater pool just feels better — “softer” is how they usually put it. That makes sense, because the water in a saltwater pool is about as salty as the water in our bodies. (A household water softener basically does the same thing — it makes “hard” water softer by making it a little salty.) So swimmers tend to feel less eye irritation and their skin is less likely to get shrivelled after being in the water for a long time.

Some also argue that you don’t get that heavy chlorine smell with a saltwater pool. But that smell — it’s from so-called chloramides, actually, and you get rid of it by adding chlorine — is the result of a poorly maintained pool and really shouldn’t occur in an outdoor pool anyway, since sunlight burns chloramides.

Is there a knock against saltwater pools? No big ones. The salt tends to cake up and scale on pool components, adding to maintenance needs. And because a saltwater pool’s pH balance often gets out of whack, it’s often necessary to pour in back-up chlorine to shock it back into shape — which undermines the arguments about this being a more “natural” way to mainatin a pool.

Environmental benefits, however, simply don’t exist. Pour the salty water on a garden and the plants will die. You can even argue that saltwater pools have a bigger footprint than a conventional pool, since the chlorine generator has to run (on electricity) for hours every day, if not round the clock.

All that said, there do exist pools filled with true ocean saltwater, but they’re very rare these days, except in Australia. They used to be more common in the U.S., according to Alison Osinski, Ph.D., of Aquatic Consulting Services. She says a handful are still in use, mostly in therapeutic spa settings, around mineral hotsprings, and on cruise ships. If you know of any, please tell us about them in the comments section.

Thanks to Ms. Osinski. Her firm, Aquatic Consulting Services, is located in San Diego and specializes in aquatic risk management and aquatic facility design, management and operation