the positive effects on food chains of supplying water in dry regions is that it won’t only help scientifically but it will also help people who lives around those regions who are in need of water since as you’ve said, it’s “dry”. The positive effect of it on food chains is that when a plant (which can be food to pollinating agents) is filled with water— once that insect decides to target on that plant— not only would it be able to take its usual benefits away but also the water in the plant.