In Lima, Peru one out of every five families doesn't have access to safe drinking water. Due to there being little rainfall but plenty of fog people have installed huge water-catching nets that condense fog into water droplets. By doing so they catch up to 10.000 liters of water per day.
What if that water could be temporarily invested in aiding a group of resilient trees to grow around each net until a self-sustaining forest took over? For the lack of knowledge of a more suitable candidate, a fast-growing, resilient species like Robinia pseudoacacia comes to mind. This video suggests a better fog-catching candidate - the Douglas fir tree. Robinia would probably grow easier in the hostile environment - so maybe a combination of suitable species that complement each other would be necessary. People could aid the process by bringing their organic waste and composting it around the nets.
When the trees grow to a sufficient height their branches and leaves would take over and condense the fog into droplets that would then drip down the trunks, into the ground. Could this eventually create a water-spring to form near the foot of the hill?
The fog-nets would then be obsolete and Lima would have a more life-friendly ecosystem. This could be repeated in other locations where hilltops are often surrounded by fog.