Water lines in Arizona single family homes are very commonly routed through the attic, where they can get very hot, so your imagined scenario isn't really that

Water lines in Arizona single family homes are very commonly routed through the attic, where they can get very hot, so your imagined scenario isn't really that far off from reality for a lot of people. I don't know how many gallons I would have to waste to get the tap to start delivering water at 50°F. I could run the faucet for several minutes and still get water that was body temperature or warmer.