How Does Water Move Through Your House?

First, we discovered how water gets to your house. Now, we’re going to focus on what happens when it gets there.

The plumbing system in your home seems complex, but it’s actually surprisingly simple. After all, home plumbing should be convenient and unobtrusive. Here’s how your plumbing manages to pull off the complex task of bringing you water every day.

How Does It Get Out of the City Main Line?

Each building connected to the city’s water has its own water main. Your home’s main line is probably near the edge of your property. Your water main receives pressurized, treated water directly from the pumping stations sending it via this line. The pressure applied to the water by the pumps gives city water enough force to travel to you.

If you live far away from the city water pumps, you may experience low water pressure. This happens because the pressure and momentum provided by the pumps partially dissipates before reaching your water line. If your home has consistently low water pressure, professionals can install a pump on your water main line, to re-pressurize water enough to circulate through your house.

How Does It Get Into My Pipes?

After entering your water main, the water moves through a large (¾ inches or larger) pipe headed toward the home. This pipe, called the water or supply line, carries water from the mainline to your house. The supply line is buried deep enough underneath the property that it won’t freeze, and it runs from the ground directly into the home. Supply lines are usually made of plastic, galvanized iron, or (ideally) copper.

How Does It Get To My Faucets?

Once inside, the water main line runs directly to your water heater. Just before connecting with the water heater, however, your main line splits into two different pipe paths. These paths are called the hot and cold service lines.  

Cold Water

The cold water service line slopes away from the water heater after splitting from the main line. Instead of sending water through the heater, cold water service lines run directly to every water appliance in the home. Plumbers install these pipes in straight lines, 90 degree angles, or slight downward slopes to facilitate easier flow.

Each water appliance has its own intake pipe, which branches off from the cold water pipes to supply the particular appliance with cold water. To get to every appliance, these pipes need to run throughout the home. If you picture a busy network of pipes when you picture home plumbing, you’re thinking of cold and hot service lines.

The Water Heater

The water that doesn’t follow the cold service line continues along the original path. The end of this path empties out into the water heater. When water from the main line floods the tank, a sensor in the base of the tank sends a message to the heating element. The heating element applies heat the tank, warming up its contents in the process.

Water heaters take time to heat water, but they also preserve a quantity of hot water in the tank for immediate use. When you “run out” of hot water after a long shower, you’ve used up your water heater’s reserves. Your water won’t be able to heat up again until more water enters the tank and the tank’s heating element activates.

Hot Water

After warming the water, the water heater shoots the it out into the hot water service lines. The hot water service lines run parallel to the cold water service lines. They never collide or intersect. If you look at exposed service pipes, you’ll notice two pairs of pipes running parallel to each other throughout the house.


When you turn on a sink’s water faucet, you’re opening the valve at the end of one of the service line’s intake pipes. Without the valve in place to block it, water flows out of the faucet and into the sink.

Every water appliance with hot and cold water settings contains intake pipes that connect with the hot and cold water supply lines. The two intake pipe connections ensure appliances can receive both hot and cold water. The only time the waters collide is when you turn both intake pipe valves at once, by turning both the hot and cold water faucets.

As you can see, a home plumbing system operates on surprisingly simple principles. But what about the last leg of the journey? We’ve covered how water gets into your house and how it gets to you, but what happens to water you’ve used? Where does it go after it’s flushed down the drain?

Next, we’ll take the last leg of the Dallas water journey by following your water out of your sink, down your drain, and on to its final destination. It’s already come a long way, but your water still has literal miles to go. Then, we’ll lay out the whole journey, step-by-step, in our “Where Does Your Water Come From?” infographic. If you ever have a question about where your water comes from, this is the only info sheet you’ll ever need to find the answer.