It's not for drinking, but for air conditioning, and more is coming as the Orlando Utilities Commission expands its chilled- water operations with a new $6 million plant going up on West Robinson Street.

OUC sells -- or more accurately rents -- cold water, much of it coming from an insulated 18 million-gallon tank brimming with water at a nippy 37 degrees. The water temperature plummets in centrifugal chillers, where spinning fans force water over tubes of coolant like socks in a rinse cycle.

The beneficiaries are big properties including shopping malls, offices and apartment buildings, which see higher utility bills but can save thousands of dollars by forgoing their own refrigeration systems. Even older buildings are better off ditching their equipment to avoid maintenance costs and replacement every 20 years or so, said Keith Rice, director of OUC's chilled-water project.

The system works on the same principle as air conditioners in homes and cars, said Rice, who monitors the process from sensors hooked to a computer that looks like it belongs in a sci-fi movie.

"It's basic science, where energy can neither be created or destroyed," he said. But energy can be traded and stored between mediums, like air and water.

It's a law of nature: Energy in the form of heat wants to warm things up that are cold. So when water close to freezing is looped through buildings, warm air blows over the coils and trades its heat. In the process, the water warms up to about 52 degrees before it heads back to OUC for another round in the chillers.

The movement from OUC's chillers and holding tanks works much the same way tap water moves through pipes. It's driven by a combination of pressure, built up in holding tanks, and pumps that move it along.

Engineer Erick Rocher recently watched the sensors with Rice at OUC's existing chilled-water plant, built on the utility's parking lot in 1999.

Outside the temperature topped 90 degrees.

The hotter it gets, the wider the system's valves open to allow more chilled water through.

"Right now, we're running at 4,500 gallons a minute," he said.

When the mercury nears 100, Rocher said, the system will run about 6,000 gallons a minute. On cooler days, say in the upper 70s, it slows to just 3,500 gallons a minute.

And like any other cooling system, the hotter it is, the higher the bill, Rice said.

Monthly tabs are calculated based on how much energy is used to cool the water and include delivery costs. The bills are about 10 percent higher than for traditional air conditioning. But that's not where companies seek savings.

Property owners save money because they don't have to buy and maintain their own cooling plants at costs that run into hundreds of thousands of dollars in upfront costs and maintenance, said Professor William Bahnfleth, director of the Indoor Environment Center at Pennsylvania State University and an expert in cooling technology.

"All those big buildings would be effectively running their own, complete refrigeration plants," Bahnfleth said. "Instead of running lots of systems, there's one centralized system. It's more efficient."

Bank of America President Ed Timberlake agreed that the initial savings to a big project such as City View apartments on Church Street more than offset the month-to-month costs.

"Cost was the factor, and this is working extremely well," Timberlake said.

OUC officials tabulated that the 20-year savings for an 18-story office building downtown would be $345,000.

Rice said the system also frees up prime real estate -- space that would normally house a building's own refrigeration plant, usually in the basement, and cooling towers on the roof.

Bahnfleth and others in the industry say the system is also better for the environment, centralizing operations and less likely to leak dangerous gases that can harm the earth's ozone layer.

"You won't have lots of smaller refrigeration plants in your downtown, with uncertain upkeep and who knows what leaking out," he said.

Chilled-water technology has been around for decades, Bahnfleth said.

About 40 cities across the United States use the technology to some extent, beginning with Hartford, Conn., in 1962 and now including Chicago and Baltimore.

Stetson University in 2003 set up its own chilled-water system in the Eugene M. and Christine Lynn Business Center. SeaWorld has its own to keep its penguins cool and comfortable.

In Orlando, Bob Haven, OUC's late CEO, began pushing for the system in 1997. A $4 million plant was built two years later.

The endeavor has expanded with satellite plants serving Lockheed Martin, the Orange County Convention Center and the Mall at Millenia. OUC serves16 customers downtown, including the First Presbyterian Church, Westin Grand Bohemian Hotel, CNL, City Hall and City View.

The new plant on West Robinson Street is expected to be operational this summer and serve more downtown customers. It can provide about 12,000 tons of air conditioning -- the equivalent of chilling about 4,000 homes, Rice said.

The endeavor reaps annual revenues of about $5.2 million, a number that is expected to grow to $6.1 million next year.

That's enough for the 81-year-old utility to gamble $6 million on a new plant.

"There's always a little bit of a risk in any new venture," said Rice.

"But this is Florida. It's hot. It's humid. The one thing everyone needs is air conditioning. I don't see it as much of a risk."