The size of the water line needed for a house depends on factors such as the number of fixtures, water flow requirements, and local building codes. Typically, residential water lines range from 3/4 inch to 1 inch in diameter. Smaller lines may be suitable for smaller homes with fewer fixtures, while larger lines are recommended for larger homes or properties with higher water demands. It is advisable to consult with a licensed plumber or contact your local building department to determine the appropriate water line size for your specific needs and local regulations.