If water is hypertonic (too salty) it can make cells swell up and burst. If it's hypotonic (not salty enough), cells shrivel up (like your finger tips when you stay in the bath tub too long.)
I just went swimming in my parents' swimming pool. I went for a dive, and forgot to exhale, so water went up my nose. Ever have that happen to you? Kinda hurts.
If you've ever tried to wear contact lenses in the pool, you'll know an even greater pain: The contact lens shrinks, squeezes your eyeball, and maybe even pops out. (The contact lens pops out, I mean. Not your actual eyeball. That would be ... well, kinda cool actually.)
All this got me thinking: Why not add some salt to the pool? Add just the right amount so the pool water is isotonic. Instead of it irritating your nose and eyes, it might even feel kinda nice.
Of course, there's the issue of chlorine. Chlorine in pools has never really bothered me, but it probably isn't too healthy either. I wonder, have we thought about any alternatives to chlorine?