From the October 2008 issue of Entrepreneur

Shrinking mountain snowcaps. Dwindling aquifers. Lakes reduced to ponds, ringed by enormous parched shores. Cities enforcing drastic water-use restrictions.

Parts of the U.S. are already experiencing these problems, and researchers who study climate change and water consumption patterns around the world say it will only get worse. Already one-sixth of the world's population lacks access to clean water. In the U.S., parts of the West and Southwest are experiencing what Gale Norton, former Secretary of the Interior, has called "perhaps the worst drought in 500 years."

Amid growing anxieties about water scarcity, hundreds of entrepreneurs are responding with products and services designed to help conserve this precious resource. Partners Jon Grobe, 36, David Morgan, 40, and Ken Scheer, 33, of Calsaway Pool Services Inc. in Tempe, Arizona, are targeting one of the Southwest's biggest water wasters: swimming pools. People in the Phoenix area have to drain their pools every two to four years because a buildup of minerals in the water blocks the effectiveness of pool disinfectants and damages pumps. Grobe and Morgan devised a patent-pending mobile filtration unit that strips minerals and other problematic substances from pool water. As a result, pool owners can use the same water for up to 12 years. "Last year, Calsaway saved the Phoenix area nearly 7 million gallons of water," says Scheer, who expects 2008 sales to reach $350,000.

Miami-based EcoloBlue makes a range of machines that use multistage filtration--free of chemicals--to create water from humidity, including a home/office model that produces around seven gallons of water per day and industrial/commercial units that produce 1,350 gallons of water per day. The EcoloBlue machines can also filter contaminated water in disaster areas. Interest in the company's products is running high around the world, especially with companies keen to include water conservation in their green-building signature. "These machines work in any environment with at least 35 percent humidity," says Henri-James Tieleman, 38, co-president and co-CEO with Wayne Ferreira, 37. They estimate that 2008 revenue will reach $1.3 million.

Soon after the Texas drought hit the landscaping around his new house, engineer Tom Watson, 53, decided to develop an irrigation system that uses internet controls and landscape modeling along with real-time, site-specific weather monitoring to reduce home, commercial and industrial water use by up to 50 percent. Now his company, Accu-Water, is 6 years old and projects 2008 revenue of $750,000 to $1 million--not to mention, many millions of gallons of water saved.