What a pressure tank does and whether you need one
A water pressure tank is a sealed container that stores pressurized water and air. When you turn on a faucet, water flows from the tank instead of directly from the pump, which means your pump doesn't start and stop dozens of times a day. The tank smooths out pressure spikes, reduces wear on your pump, and gives you water pressure even during a brief power outage.
You need a pressure tank if you have a well pump or a private water system. If you're on city water, you almost certainly don't need one—the municipal system already maintains pressure for you. If you have a well and no tank, your pump is cycling on and off constantly, which shortens its life and can cause pressure to drop noticeably when multiple fixtures run at once.
Installing a pressure tank is a plumbing job that involves cutting into your water line, adding fittings, and connecting the tank with proper air charge and water volume. It's doable for a confident homeowner with basic plumbing skills, but if you're not comfortable working with water lines or pressurized systems, hire a licensed plumber. A mistake here can lead to leaks, loss of pressure, or damage to your pump.
Key Takeaways
- A pressure tank stores water under pressure so your pump doesn't run constantly, and you need one if you have a well system.
- Tank size depends on your pump's flow rate and how often you want the pump to cycle—a 20-gallon tank is common for household wells, but larger homes may need 40 or 60 gallons.
- The tank must be charged with air to the correct pressure before installation, and that pressure is usually 2 pounds per square inch (PSI) below your pump's cut-in pressure.
- Installation involves shutting off the pump, draining the system, cutting the water line, and connecting the tank with a tee fitting, check valve, and pressure gauge.
- After installation, you'll need to adjust your pressure switch settings and bleed air from the lines before the system is ready to use.
Choosing the right tank size for your well
Tank size is measured in gallons and depends on two things: how much water your pump delivers per minute, and how often you're willing to let the pump cycle. A pump that cycles too frequently wears out faster and uses more electricity.
Most household wells pump between 5 and 15 gallons per minute. A rough rule is to choose a tank size equal to three times your pump's flow rate in gallons per minute. So a 10-gallon-per-minute pump would call for a 30-gallon tank. In practice, 20-gallon tanks are common for small homes, 40-gallon for medium homes, and 60-gallon or larger for homes with multiple bathrooms or high water demand.
If you're not sure of your pump's flow rate, you can measure it: turn on an outdoor faucet at full flow, time how many seconds it takes to fill a 5-gallon bucket, and divide 300 by that number. A bucket that fills in 20 seconds means your pump delivers 15 gallons per minute.
Larger tanks are not always better—they take up more space and cost more—but they do reduce how often your pump runs. If your basement or utility room is tight on space, a smaller tank is acceptable as long as you accept that the pump will cycle more often.
Pre-charging the tank with air
Before you install the tank, it must be charged with compressed air. This air cushion is what allows the tank to store pressure and release water smoothly. An uncharged tank will fill with water, offer no pressure benefit, and can damage your pump.
The correct air pressure is usually 2 PSI below your pump's cut-in pressure. If your pump is set to cut in at 40 PSI (a common setting), you'll charge the tank to 38 PSI. Check your pump's documentation or look at the pressure switch to find the cut-in setting.
To charge the tank, use a bicycle pump or an air compressor with a pressure gauge. The tank has a small air valve on top, similar to a car tire valve. Unscrew the cap, attach your pump, and inflate to the correct pressure. Check the pressure with a tire gauge to be sure. If you overcharge, press the valve to release air until you reach the target.
Many new tanks come pre-charged from the factory, but the charge can leak away during storage. Always check the pressure before installation, even if the tank is new.
Shutting down your system and draining the line
Before you cut into your water line, you must turn off the pump and release all pressure from the system. A pressurized line can spray water and cause injury.
Locate your pump's power switch or breaker and turn it off. Then open the lowest faucet in your house—usually an outdoor spigot or a basement sink—and let water run until it stops. This drains the line and releases pressure. If you have a pressure gauge on your system, watch it drop to zero.
Leave the faucet open while you work. This prevents air from being sucked back into the line as you cut and fit the new tank connection.
Cutting the line and installing the tee fitting
The pressure tank connects to your water line through a tee fitting—a three-way connector that splits the line so water can flow to the tank and to the rest of your house.
Identify where your pump's discharge line runs. This is the pipe that carries water from the pump toward your house. Choose a spot within a few feet of the pump—the closer, the better. Mark the line and use a pipe cutter to cut straight across. If the line is copper, a tubing cutter works best. If it's PVC or PEX, a hacksaw or PEX cutter is fine. Make the cut square and smooth.
Dry the cut ends completely with a clean cloth. If you're working with copper, you'll need to solder the tee fitting in place. If you're not comfortable soldering, this is the point to call a plumber. For PVC, use PVC cement to glue the tee. For PEX, use a crimping tool and crimp rings to find the fitting.
The tee should be oriented so one outlet points toward the tank and the other continues toward your house. The third outlet (the stem) connects to the pump.
Connecting the tank with a check valve and gauge
From the tee fitting, run a new section of pipe to the tank. This run should include a check valve positioned between the tee and the tank. The check valve allows water to flow into the tank but prevents it from flowing backward into the pump when the pump shuts off.
Install the check valve with the arrow pointing toward the tank. Use the same connection method as your main line—solder for copper, cement for PVC, or crimp for PEX.
Connect the other end of the pipe to the tank's inlet port, usually marked with an arrow or labeled "inlet." Use a compression fitting or threaded adapter, depending on your tank's connection type. Wrap the threads with plumber's tape (also called PTFE tape) to prevent leaks.
At the tee fitting, also install a pressure gauge on the outlet that continues toward your house. The gauge lets you monitor system pressure and troubleshoot problems later. Wrap the gauge threads with plumber's tape and screw it in firmly.
Adjusting pressure settings and bleeding air
Once the tank is connected, turn the pump back on and let the system fill. Water will flow into the tank and build pressure. Watch the gauge as pressure rises.
Your pump has a pressure switch that turns the pump on and off. The switch has two settings: cut-in pressure (when the pump starts) and cut-out pressure (when it stops). Most household systems are set to cut in at 40 PSI and cut out at 60 PSI. If your settings are different, you may need to adjust them—check your pump's manual for instructions.
As the system pressurizes, air will be trapped in the lines and faucets. Open each faucet in your house one at a time and let water run for 30 seconds to a minute. This bleeds trapped air and prevents sputtering. Start with the faucet closest to the pump and work your way to the farthest one.
Once all faucets run smoothly without sputtering, your system is ready. The pump should cycle on when pressure drops to the cut-in setting and off when it reaches the cut-out setting. If the pump cycles too frequently or pressure is unstable, the tank may be incorrectly charged or the wrong size for your pump.
When to call a plumber instead
Install the tank yourself if you're comfortable soldering copper or using PVC cement, and if your pump setup is straightforward. Call a plumber if your pump is in a confined space, if your water line is buried or hard to access, or if you're unsure about your pump's pressure settings.
A plumber can also help if you're upgrading from an old tank or if your system has complications like a water softener or filter that affects where the tank should connect. The cost of a professional installation is usually $300 to $800 depending on your location and system complexity, but it's worth it to avoid leaks or pressure problems that could damage your pump.
Frequently Asked Questions
Can I install a pressure tank on a city water system?
No. City water systems maintain their own pressure, and adding a tank can actually cause problems by interfering with backflow prevention and creating stagnant water. Pressure tanks are only for private wells and similar systems where you control the pump.
What happens if I charge the tank with the wrong air pressure?
If the air pressure is too low, the tank fills with water and offers little pressure benefit. If it's too high, the pump has to work harder to push water in, and the tank may not accept a full charge of water. Either way, your pump cycles too often and wears out faster. You can fix it by releasing or adding air until the pressure is correct.
How often do I need to check the tank's air charge?
Check it once a year, usually in spring before heavy water use begins. Air can slowly leak from the valve over time. If the pressure has dropped more than a few PSI, recharge it. If it drops significantly every few months, the valve may be leaking and the tank may need replacement.
Can I install a pressure tank myself if I've never done plumbing before?
If your water line is accessible and you're willing to learn soldering or PVC cement, yes. Watch videos on the specific connection method first, practice on scrap pipe, and take your time. If you're not confident, hire a plumber—a leak or incorrect installation can cost more to fix than the installation itself.
What size tank do I need if I have a very small well pump?
Even a small pump benefits from a tank. A 5-gallon-per-minute pump can use a 15 or 20-gallon tank. The pump will cycle more often than with a larger tank, but it's still better than no tank at all. Avoid tanks smaller than 15 gallons unless your space is extremely limited.