The original question here was "...find potable water during a flood?"

FLOOD. That means lots of water saturating the soil, not the Mohave in summer.

While sunlight is necessary for transpiration, so is moisture in the soil. If there isn't much moisture in the soil, you aren't likely to get a lot of transpiration. But in the case of flooding, the results could be far different.

That could be an interesting experiment. I may have to do something about that.

The best part of transpiration under flood conditions is that the water is clean and ready to drink (assuming you didn't use toxic trees).

Although collecting water from rainfall from a clean surface would be simpler.

Edited to add: Someone did an experiment at Practical Survivor in a non-desert situation, in the sun, and got half a cup of water from one bag in one day. But would that have increased after a flood, from saturated soil?

Sue

Here is some info from the Survival Mom site about collecting water during/after a flood.

Survival expert Peter Kummerfeldt says, "It is not uncommon to find two or three cups of water, and sometimes much more, has accumulated over a six-to-eight hour daylight period..."

Sue