According to NASA, the mass of all asteroids in the Solar system is less than the mass of the moon. By the way, this is why there can be no life on them, because they are not able to hold the atmosphere.
Although a layer of ice was found on several asteroids, as well as channels from water.
How ice forms on asteroids is still unknown for certain, but there is a theory that small asteroids, crashing into one large one, tear a layer of ice from its surface. The force of the impact turns the ice into water, which flows in veins throughout the surface.