On average, the temperature of tap water is roughly 13 degrees Celsius. The temperature of tap water is dependent on the temperature of the pipes, which is dependent on both the temperature of the house and the outdoor environment.
Tap water temperature is much like room temperature in that it depends on the local conditions. Because frozen pipes block water flow, it is not possible for tap water to be any colder than freezing. If the heat ever reached a point that the pipes would cause the water to boil, it also would not be possible to have water flow.