In the days when indoor plumbing was less common than it is today, it was usual for advertisements for houses to mention "hot and cold running water" if the house had proper indoor plumbing (or just "cold running water" if there were piped cold water, but no water-heater). As a result, "hot and cold running water" came to be used as a casual or joking phrase to mean that whatever was being discussed had all the features one might expect to find.
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