Very few houses in the U.S. get their water supply from storage tanks or wells. Most rely on the municipal water supply, which is pressurized (unlike other sources that mainly rely on pumps or gravity for pressure).
The municipal water supply distributes water to different homes in the jurisdiction. Each house gets its supply through a water main that is usually located at the edge of the property next to the street. There is a main water valve in the area where the home supply is fed by the municipal line. The purpose of the main water shut off valve is to turn off water to the home when repairs are being done in the water pipes and devices. Homeowners are advised to be familiar with the location of the main shut off valve in order for them to cut the water supply in case of a broken or burst pipe at home. This helps avoid flooding and resulting water damage.
The municipal utility company bills each home based on the amount of water consumed as measured by the water meter. Beyond the water meter is the main water line that extends toward the house. The typical size of the main line is ¾ inches or bigger. The main water line is usually buried under the ground to prevent freezing, especially in areas where temperatures dip significantly in winter.
The main water line is fitted with a back-flow preventer on the exterior of the house. The purpose of this device is to prevent contaminated water from entering the supply line when the pressure is low. There is another device attached to the line known as a pressure reducer. This will allow the homeowner to reduce water pressure going into the house to prevent damage to the fixtures.
The water line is split once it enters the home. One line goes straight to the water heater to ensure adequate pressure. The other supplies cold water to the rest of the house.