It's a common misconception that a saltwater pool doesn't use chlorine. All a salt system does is convert salt water (NaCl) to chlorine (NaClO) and hydrogen gas using a electrolysis. when the chlorine is used (oxidizes undesired contaminants) it breaks back down to saltwater. Cost wise it is basically the same as using liquid or powdered chlorine as the electrolysis cell has to be replaced every 3 to 5 years and cost about the same as 3 to 5 years of chlorine product. Also the salt levels required to run a salt water pool are very low compare to sea water (3,000 ppm to 30,000 ppm) so they are not supposed to be very corrosive. All commercial pools are required to use chlorine as an oxidizer and have to have a monitoring system, usually an ORP meter and feeder, that will dispense chlorine as it is depleted from the water. Most water parks use chlorine gas to disinfect the water I believe its more cost effective. I would much rather swim in a commercial pool with a chlorine level of 10ppm than with none as the amount of bacteria and parasites in the water with a lot of bathers would scare anyone. UV is a great way to kill things too especially microorganisms that chlorine can take longer to kill. Look up Cryptosporidium and you'll be very wary of any public pool. Don't get me started on spas you're basically bathing in everyone's sweat among other things. Always bring test strips to make sure the water is safe.