Why you don't try a very old (neolithic ! ) system of water catchment: Called "dew ponds", "cloud ponds" or "mist ponds" (in German "Tauteich").
These ponds are thermally insulated to the ground. At night the water looses temperature due to heat radiation faster than the ground around. So air humidity (from fresh sea air or from humid air from the warmer ground) above the water level can condense and fill up the pond.
You can find a description at
o
English Wikipedia or
o
German Wikipedia.
Have a look to
this exciting website about or look for pictures (and other websites) at Google.
Here at Google Books.
The ponds are made of loam/mud/clay, then straw and then clay and a fireplace. The fire made a glaze firing at the upper layer of clay, so the ponds became more durable.
You could build or experiment a modern dew pond with pond liner (PVC, rubber) and foam or foam-perlite as insulation and additional during the day with insulation/sun shield at the water-surface (protection against evaporation). Why not?
Or you take an insulated (!) swimmingpool with a modern insulating cover mat. For swimming the mat is open during the day and the sun warms up the pool water. For water catchment you have to manage it all the time in opposite procedure: Close the mat during the day and open it during night to cool the water and to catch the humidity of the air.
