The European Hershel infrared space telescope has detected water vapor emissions from Ceres,  the largest asteroid (it’s also called a dwarf planet):

From the last item:

Scientists believe Ceres contains rock in its interior with a thick mantle of ice that, if melted, would amount to more fresh water than is present on all of Earth. The materials making up Ceres likely date from the first few million years of our solar system’s existence and accumulated before the planets formed.

Until now, ice had been theorized to exist on Ceres but had not been detected conclusively. It took Herschel’s far-infrared vision to see, finally, a clear spectral signature of the water vapor. But Herschel did not see water vapor every time it looked. While the telescope spied water vapor four different times, on one occasion there was no signature.

Here is what scientists think is happening: when Ceres swings through the part of its orbit that is closer to the sun, a portion of its icy surface becomes warm enough to cause water vapor to escape in plumes at a rate of about 6 kilograms (13 pounds) per second. When Ceres is in the colder part of its orbit, no water escapes.

Artist’s impression of Ceres

NASA’s Dawn spacecraft will reach Ceres in the summer of 2015.  Launched in September 2007, Dawn investigated the asteroid Vesta until July 2012 and then began moving towards Ceres, where it will have a lot of interesting science to pursue.

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Here’s a discussion of the Ceres finding and teh significance of so much water among the asteroids: Why It Matters That There’s So Much Water in the Asteroid Belt – Popular Mechanics

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Asteroid specialist Humberto Campins spoke about the Ceres findings with David Livingston and John Batchelor on Wednesday : John Batchelor Hotel Mars, Wednesday, 1-29-14 – Thespaceshow’s Blog