Conditions required for liquid water is a temperature and pressure above the triple point of water. The surfaces of comets are certainly warm enough, based on measurements taken by probes and earth based. Pressure only needs to be .006 Atmospheres. Since jets are powered by the thermal energy absorbed by the surface, there must be some gas pressure being held in the surface- ie. a subsurface atmosphere. Thus liquid water could flow in the microgravity environment. Some Stardust probe sample return minerals found can only be formed in liquid water. Deep impact probe excavated clays which are suggestive of liquid water. Capillary action, microgravity, centrifugal forces and internal wind would affect the movement of water and material inside the comet.
Long live the wet comet model.
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