This was an interesting read.

Water's great, but it doesn't hurt to have/keep ice in the HZ either. :}

Even Mercury has ice (albeit, it may be very old):

[How did the ice get there originally?
There are only two significant sources for ice on Mercury: meteorite bombardment and planetary outgassing. Meteorites, especially in the past, potentially carried large amounts of water to Mercury's surface. Outgassing of water from the planet's interior could also provide a non-negligible flux of water to the surface, although this is speculative. The permanently shadowed regions near Mercury's poles should act as "cold-traps" so that any water which found its way to these regions would freeze on the surface and remain. (The possibility that the ice is relatively uncontaminated may indicate that each deposit was laid down in one or a small number of rapid events (6), such as a large comet impact.) Meteorites which impacted near the poles and water which outgassed in that region could have been easily trapped. Water originating away from the poles would behave as individual, randomly moving molecules, some of which could migrate to the poles and become trapped there (6). There are mechanisms for potential loss of ice, however. These include photodissociation, solar wind sputtering, and micrometeoroid gardening. The effects of these processes are not well-understood.]

From:
http://nssdc.gsfc.nasa.gov/planetary/ice/ice_mercury.html