Just out of interest, why does the tap water get so hot in Summer? Surely if it is "mains" water it travels in pipes quite deep underground and the temperature is fairly stable. If it is stored in a tank in the house then it's a different matter. I don't know how water supply works in the US but in the UK there is "mains" water that comes into the house for drinking and then everything else (toilets, baths, basins etc) is gravity fed from a tank in the loft. I always run the tap to purge what is in the pipes in the house until it runs cold from the water underground. Probably too geographically specific, climate included as well as plumbing.
It depends where you are. Typically, the water lines are buried below the frost line so they do not freeze in the winter. The purpose is to keep the water lines from freezing and/or breaking - having cool water in the summer is merely a side-effect. I suspect it is the same reason in your area.
In areas that do not get freezing winter temperatures, they don't always bury the lines deep enough to keep them cool, especially if the area is very rocky. It is seen as an added expense.
I live in Northeast Ohio, and our lines are buried. Nice cool water year-round. Homes feed directly off of the buried water lines. Tall buildings, like apartments, will pump water from the mains to a large tank on top to feed the building like you mention; there would not be enough pressure otherwise. Many people in the U.S. still have wells, but these are usually areas that do not have easy access to a public water infrastructure (some rural areas, or places where it is too difficult or expensive to run mains).
I have no idea how long my city has had public water - at least 50-60 years. A home behind me kept using a well for a very long time, and finally tied into the mains probably 20 or 30 years ago. I only know this because I smelled a foul odor one very hot summer day about 5 years ago. I thought it was our dog's "fertilizer" fermenting in the heat, but learned our neighbor had kept his well to water his lawn and garden.