Why? One house is behind another. There is no reason why the main pipe couldn't go straight from the street in front of house number one, under the house, and then straight on to house number 2. Now, if the houses were side by side, or the water line come from the side of the houses, then I agree that there would be a T. However these houses are described as one being in front of the other, with the front house being there first.

