How your plumbing works

Your home's plumbing is really two systems working side by side. Knowing the basics makes it easier to spot problems early, and to know what we're talking about when we explain a repair.

The big picture

Two systems: water in, water out

Clean water and used water never mix. One system pushes water in under pressure. The other carries it away using gravity.

The supply system

Brings clean water from the city main into your home. It's always under pressure, which is what pushes water up to your second-floor shower the moment you turn the handle. Cold water goes straight to your fixtures. A branch fills the water heater, which sends hot water out on its own set of pipes.

The drain, waste, and vent system

Carries used water out of your home. There's no pump behind it. Drain pipes are sloped so gravity does the work, and vent pipes through the roof let air in so everything flows smoothly.

Water in

Follow the water into your home

  1. 1

    City water main and your service line

    A buried pipe called the water service line connects the city's main under the street to your house. In Lincoln, it has a valve near the property line called the curb stop. Except for the meter, repairs to the service line are the property owner's responsibility. For the full rules, see the City of Lincoln Water Service Manual.

  2. 2

    Water meter and main shut-off valve

    Where the line comes into your home, you'll find the meter and the main shut-off valve. This is the valve to close in an emergency, like a burst pipe. Make sure it turns. If it doesn't work, Lincoln Water System can shut off your water at the curb stop (402-441-7571).

  3. 3

    Pressure reducing valve (if you have one)

    Most plumbing codes require a pressure reducing valve when city pressure is over 80 psi. The EPA's WaterSense program recommends 45 to 60 psi for a home. Too much pressure wears out pipes, faucets, toilets, and appliances, and a failing valve can cause banging pipes or pressure swings.

  4. 4

    Cold lines and the water heater

    From there, the pipe splits. Cold water runs straight to sinks, toilets, showers, and outdoor faucets. A branch feeds the water heater, and hot water travels back out alongside the cold lines to the fixtures that need it.

  5. 5

    Shut-off valves at each fixture

    Most sinks and toilets have their own small shut-off valves, so a single fixture can be repaired without turning off water to the whole house.

Up close

Your water heater and expansion tank

That small tank sitting on top of or next to your water heater does an important job. Here's why it's there.

Water grows when it's heated

Water expands about 4% as it heats up. A full 50-gallon water heater ends up holding about 52 gallons' worth of water. Those extra 2 gallons need somewhere to go.

Most homes have a "closed" system

Check valves and backflow preventers keep your water from flowing back into the city supply. That protects the public water, but it also means expanding water can't escape back out to the street. Without somewhere to go, it builds pressure inside your water heater and pipes.

How the expansion tank helps

Inside the tank, a rubber diaphragm separates a pocket of compressed air from a space that fills with water. As hot water expands, it pushes into the tank and squeezes the air like a spring. When pressure drops, the air pushes the water back out. Most home expansion tanks hold about 2 to 4 gallons.

What happens without one

  • Extra wear on the water heater. Constant high pressure stresses the tank until it leaks. A leaking tank has to be replaced.
  • A dripping relief valve. The temperature and pressure relief valve (T&P valve) lets out water when pressure gets too high. It's a safety device, not meant to run all the time, and it wears out early if it does.
  • Code and warranty problems. Many areas require an expansion tank with a new water heater on a closed system, and some manufacturers' warranties exclude damage caused by thermal expansion.

Signs your expansion tank has failed

If the tank is full of water, the rubber bladder inside is broken and the tank needs to be replaced. A T&P valve that drips or a water heater that's leaking are also worth a call.

What about tankless water heaters?

Most tankless water heaters don't need an expansion tank. Some do, such as when there's a hot water recirculation line or the system includes a storage tank. Local code decides.

Not sure if you have one, or if it's working? Call 402-466-5300 and we'll check your water heater and expansion tank.

Water out

Follow the water out of your home

  1. 1

    Fixture drain and P-trap

    Under almost every sink, tub, shower, and floor drain is a U-shaped pipe called a P-trap. It holds a little water that seals the drain and keeps sewer gas out of your home. Toilets have a trap built into the bowl.

  2. 2

    Branch drains

    Drain pipes slope downhill, usually about 1/4 inch per foot for smaller pipes, so gravity carries water toward larger pipes.

  3. 3

    Vents through the roof

    Those pipes sticking out of your roof are vents. They let air into the drain lines so water flows freely and doesn't suck the water out of your traps. A blocked vent can cause gurgling, slow drains, and sewer smells.

  4. 4

    Main stack and main drain

    Everything flows into the main stack, a large vertical pipe, and then into the main drain that leaves your home near the foundation. Cleanouts give plumbers access to clear clogs.

  5. 5

    Sewer service line to the city main

    A buried sewer line runs under your yard to the city's sewer main. In Lincoln, the city maintains the main, but the private service line connecting your home is the property owner's responsibility. Tree roots and grease are common causes of backups.

Quick troubleshooting

What your plumbing is telling you

Sewer smell from a drain you rarely use

The water in the trap may have dried out. Run water for a minute to refill it. If the smell sticks around, call us.

Gurgling or several slow drains

Could be a blocked vent or a clog in the main line. A camera inspection shows exactly what's going on.

Dripping water heater relief valve

Often a sign of too much pressure or a failed expansion tank.

Banging pipes or pressure swings

Your pressure reducing valve may need to be adjusted or replaced.

Water meter moving with everything off

There's likely a leak somewhere, possibly in the service line.

Water backing up in a basement drain

Usually a blockage in the sewer service line. Stop using water and call us.

Want simple checks you can do yourself? See our home maintenance tips and ways to protect your home.

Learn more

Sources and helpful guides

Have a question about your plumbing?

Call 402-466-5300, text 402-601-4490, or email services@jtkservicesinc.com. Ask about our senior citizen, veteran, active military, and first responder discounts.

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