"would the pants material be able to "hold" the water ?"
A tightly-woven natural fabric like cotton would probably do very well. When the fibers get wet, they tend to swell, which I believe is how the old canvas tents shed water (long before the days of silicone).
And when I was a kid, my father had this fabric bag with a handle that you could fill with water and hang from the car's radio antenna. I don't know if it was lined with rubber or not, but the water did ooze out of it, and evaporation kept it cool. Of course, eventually, all your cool water would eventually weep out and evaporate, but it would hold it for at least a day, IIRC.
Sue