How Chlorination Works
The purpose of adding chlorine to a swimming pool's water is to kill microorganisms that may cause health problems for swimmers. In a traditionally chlorinated freshwater pool, chlorine-based disinfectants are added to the water, and the chemicals in those disinfectants, typically hypochlorous acid and hypochlorite, kill the potentially harmful microorganisms.
When the disinfecting chemicals react with organic compounds in the water such as sweat, body oil and urine, they are converted to compounds called chloramines. As more and more of the germ-killing chlorine in the water is converted to chloramine compounds, the sanitizing power of the disinfectant is reduced, and the chloramines produce the distinctive chlorine smell that may be irritating to swimmers. In a traditional system, the only way to bring the water chemistry back into balance and eliminate chloramines is to add a substantial additional amount of free chlorine.
The Saltwater Difference
The chemical process of disinfection is the same in both traditionally chlorinated pools and saltwater pools. In both types of pools, the free chlorine added to the water kills microorganisms, and in both cases, the reaction of the chlorine with organic compounds creates smelly chloramines.
The chlorine generator in a saltwater pool does increase the salinity of the pool water, but the resulting salt concentration in the water is much less than that of sea water, and swimmers are unlikely to notice much of a difference in the feel, smell or taste of the water.
Costs and Convenience
The advantage of a saltwater pool over a traditionally chlorinated pool is largely one of convenience. Because the chlorine generator constantly adds free chlorine to the pool water, there is no need to manually add liquid chlorine or chlorine tablets to the water. The constant supply of free chlorine in the water may also help to keep chloramine levels in check and reduce the need to "shock" the pool with high doses of chlorine.
Saltwater pool systems are expensive to buy and install, however, and although you'll eventually save money by not having to purchase chlorine, the cost of the system will probably be roughly equal to the maintenance of a traditionally chlorinated pool over time. You'll have to occasionally add salt to the system, so a saltwater pool is not without supply costs or maintenance chores. Because saltwater is corrosive, there will also likely be costs associated with replacing parts of the system that are damaged over time, and the electricity used to run the system may be as much as $150 per year, as of the time of publication.