Frozen soil around the moon's poles may contain as much as 250 billion gallons of water, enough to fill the need of U.S. cities for 10 days, according to data from a spacecraft orbiting the moon.

In a study published Friday in the journal Science, researchers said the Lunar Prospector spacecraft probing the moon's surface has found evidence of up to 10 billion tons of water locked into deeply shaded pockets of lunar soil."There is an abundance of hydrogen at both lunar poles, and we interpret that to mean there is water there," said Alan Binder, chief scientist for the Lunar Prospector spacecraft. "There is at least 1 billion tons of water, but there could be as much as 10 billion tons."

It is estimated that U.S. cities use about 25 billion gallons of domestic water a day. Thus, the 250 billion gallons would represent enough to fill the washing, flushing and watering needs of every municipal home in America for 10 days.

Binder said it would certainly be enough to build a colony on the moon's surface and to operate a rocket service station for journeys beyond.

"We knew from the Apollo missions that we could go to the moon and build a base there, but we would have to take our water and fuel with us," Binder said.

The deposits of water or hydrogen, he said, are "an enabling resource. You could build a colony without it, but this really makes it a lot simpler."

In addition to sustaining life in such a colony, water also can be used for rocket fuel by breaking it into its constituent chemicals - hydrogen and oxygen. Propellant for the main engines on the space shuttle, for instance, is hydrogen and oxygen.

Paul Spudis, a researcher at the Lunar and Planetary Institute in Houston, called the discovery significant. "We've debated for 30 years whether or not there is ice on the moon, and now this shows there is," Spudis said.

Comets smashing into the moon over millions of years probably deposited the water, Binder and Spudis said.

Spudis was on the science team of an earlier lunar mission, the Clementine spacecraft, that found radar indications of water on the lunar south pole. Now, he said, the presence of lunar water has been confirmed by two different research methods.

"This makes colonizing the moon a lot more attractive," said Ed Weiler, a space scientist at NASA. "I think before we colonize Mars, we need to colonize the moon for practice. So from that perspective this is a major discovery."

NASA currently has no plans to return people to the moon.