In the winter season, the morning temp. on the earth's surface is very low. But the inner core of the earth is always hot. We know, well water is absorbed from deep inside the ground. At that surface, water absorbs the heat from the earth's core and remains hot. When the same water is brought to the surface, the temp. of water is higher than that of surroundings. So, well water is felt to be warmer in the morning during the winter.