Wow
I never thought about hot the underground water line can get.
Not sure how long a run you have on your property, but maybe laying the main deeper under ground? It would be a bit cooler there, at least until the surrounding earth warms up from the water.
Splitting the main into a few pipes running parallel, at a certain distance from each other, would be better, but the cost would go up.
Another idea would be an underground tank, deep enough to cool the water somewhat, large enough to hold 1-2 days' worth of your water usage. The tank could be air-tight and pressurized, so the water just flows through, without the need for additional pumps.
Not sure whether this might not increase the risk of microbes in the water.