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The Three Types of Plumbing Systems in The Home

Every plumbing system includes supply lines, fixtures, and drains. Each of these parts help supply water and remove waste from the home. Understanding how these three systems work will shed some light on why things go wrong and how to make the repairs.

  1. Supply Line System

The supply line system is made up of pipes, valves, and fittings that carry water throughout the home’s plumbing system. A home’s water supply may come from a reservoir, municipal water system, or a private well.

Water passes through a curb valve near the street and enters into a water meter and main shutoff valve, which is located on the side of the home or in a basement or crawl space.

Water pressure helps push water through the supply line system. The pressure needs to be just right — typically between 40 and 60 PSI — to ensure water doesn’t cause pipes to crack or burst. Low water pressure can cause poor water flow, while high pressure can damage pipes.

Cold and hot water lines run parallel to each other, about six inches apart.

  1. Plumbing Fixtures System

Plumbing fixtures include the sinks, showers, bathtubs, toilets, sprinklers, dishwashers, and washing machines. These fixtures may connect to the supply line and/or the drainage system. 

Near most fixtures is an air chamber, which is a capped vertical pipe that traps a column of air to cushion onrushing water when the faucet is turned off. This chamber prevents a sudden increase in pressure within the water supply system that could lead to a water hammer, potentially bursting open pipes and fittings.

  1. Drain-Waste-Vent (DWV) System

This system is the least visible part of the plumbing system and the most heavily regulated by housing and plumbing codes. 

The drain system relies on gravity to remove wastewater from the home. Each drainage fixture is connected to a drainpipe by a P-trap, which fills with water to prevent sewer gas from entering the home.

The water in the trap prevents small animals and sewer gas from causing problems. Every time a toilet is flushed, the water in the trap is replaced.  

Each branch drain connects to a larger vertical pipe called a stack. The stack travels through the roof to vent sewer gas and maintain proper air pressure in the system.