Or freeze the bottles of h20, in the SoCal sun here in the summer, it melts just fast enough to keep me hydrated and slowly enough that it stays cold down to the last drop.
That's why god invented the disposable water-bottles (and, of course, 7-11 equivalents worldwide like the Polish Żabka, The Little Frog)
OSHEE (for Bike Riders): An isotonic sports drink in a 0.7 litre disposable bottle of the bike water-bottle size. A product of Poland.
I actually buy OSHEE Zero, the sugar-free version.
I had the down tube water bottle holder and the 2 bottle holder under the seat of my road bike. I would freeze the 2 bottles that went under the seat. As they thawed they were nice and cold! I've tried all the fancy insulated bottles and just found that freezing a regular bottle works great.
thoughts of a peltier based solid state refrigerator? combined with good insulation of course. decent for weight but would eat your accessory battery which gets charged from HV drive battery.