It started with cans and bottles, evolved to include bamboo flooring and nontoxic paints, and now the latest focus of the eco-friendly movement is...swimming pools. Installations of in-ground residential pools have dropped by double digits in each of the past three years, according the Association of Pool & Spa Professionals, but installers say there s one bright spot in the market sales of green pool equipment. Some of the options:

Saline pools, which are about 10 percent as salty as seawater, have become increasingly popular with people looking to minimize chlorine use. Chlorine is still present it s created when the saltwater passes through a salt chlorine generator but pool owners don t have to buy or handle it. Proponents of salt pools also say the water smells better and is easier on eyes and skin, not to mention wallets. With salt costing $2 to $10 a month, a saline system is cheaper to maintain than a standard chlorine system. One downside: Some owners report corrosion of nearby decks or furniture.

Cut Chemicals

Looking to reduce chlorine even further? Some pool owners are turning to ultraviolet light filters, which reportedly help shrink a pool s chemical content by about 70 percent. These systems work by filtering the water through a chamber that kills organic matter by blasting it with powerful UV light. But the special bulbs, which cost as much as $400 apiece, must be replaced every couple of years. A slightly more affordable option is Zodiac Pool Systems Nature2 CF, a $102 cartridge that can be dropped into a standard pool filter and cleans the water using minerals; each cartridge lasts about four months.

Save Your Energy

Of course, going green isn t just about what s in the water. A variable-flow circulation pump, which filters more slowly than most, uses about six times less electricity and saves up to $500 a year, says Dana Anderson, president of Oregon-based Anderson Poolworks. Using sun power can also help conserve; solar pool covers reflect rays and minimize evaporation, while solar heating systems all but eliminate power bills. They re not cheap: The heaters start at about $3,000. But according to the U.S. Department of Energy, they can pay for themselves in as little as two years and typically last 10 or more.