For facts and figures see Fog as a Fresh-Water Resource: Overview and Perspectives where they say that depending on the situation, fog collectors can collect between 1 and 70 liters per m2 per year, with typical yearly averages for operational projects, between 3 and 10 liters per meter square per day averaged over the year.
Your zeppelins could be used to suspend larger nets, up to thousands of meters.
A 1000 meter high mesh, width of say 10 meters, stretching from the ground up to your zepellin, by those figures would typically collect between 30,000 and 100,000 liters of water per day on a suitable site.