The streaks themselves are not necessarily comprised of water, be it solid, liquid, pure, or diluted.

The streak-sources are generally located along an even line along the face of a slope or cliff, indicating a layer of probable permafrost. Breakdown, whether by thaw, by sublimation, and/or by ice-erosion will result in some form of disturbance. Whether by the condensation of seeping/escaping moisture that makes minute dust particles heavy enough to break away and tumble into a ravine, or simple material movement through sublimation, the streaks are likely resultant of a chemical reaction in this layer of supposed frost which knocks material loose. Whether dislodged through the rapid expansion of underground gasses during the warmer months, or weighted with the addition of some supposed moisture, the released material will tumble down the slope/cliff, resulting in streaks that appear darker than the surrounding material. Over time, redusting will settle a new layer, covering and smoothing these streaks, as they appear to "fade away."

I strongly doubt the streaks are actual water trails, as this would suppose water in extreme abundance everywhere, and in such an impure state as to survive in liquid stream sometimes kilometers long -- but we have little evidence that this could be the case. We do, however, have very strong evidence that both dust and gravity exists just about everywhere in the planet.

Dan