What pressurizing a water tank means and why you might need to do it
Pressurizing a water tank means adding air pressure inside the tank so water flows out with force when you open a tap or turn on a shower. Most household water tanks need between 40 and 60 pounds per square inch (PSI) to work properly. If your water pressure has dropped, the tank may have lost air pressure, and you can restore it without calling a plumber.
Water pressure drops for three main reasons: the air pocket inside the tank has leaked out, the tank has filled completely with water and no air remains, or the pressure relief valve has opened and released the air. You can check and fix the first two yourself. The third usually means the tank is old or the valve is failing.
Before you start, turn off the pump that fills the tank and drain some water from the lowest tap in your house. This gives you room to add air and makes the work safer.
Key Takeaways
- A water tank needs air pressure between 40 and 60 PSI to push water through your pipes; if pressure has dropped, the air pocket inside may have leaked out.
- You can check the current pressure with a tire pressure gauge on the air valve at the top of the tank, the same type of valve found on a car tire.
- Add air using a bicycle pump, a hand pump, or an air compressor, depending on how much pressure you need to restore.
- If the tank refills with water and pressure drops again within days, the air valve is leaking and the tank will need to be replaced or repaired by a technician.
- Tanks with a waterlogged condition — completely full of water with no air pocket — need to be drained and refilled to restore the air space.
How to check the current pressure in your tank
Find the air valve on top of the tank. It looks like the valve on a car tire and is usually a small metal stem sticking up from the tank cap. Some tanks have it on the side instead. The valve will have a small cap you can unscrew by hand.
Unscrew the cap and attach a tire pressure gauge — the same tool used to check car tire pressure, available at any auto parts store or hardware store for under $10. Press the gauge onto the valve stem firmly until you hear a small hiss of air. The gauge will show a number in PSI. Write this number down.
If the gauge shows zero or very low pressure, the tank has lost its air pocket. If it shows pressure between 40 and 60 PSI, your tank pressure is normal and low water pressure may come from a different cause — a clogged filter, a failing pump, or a problem in your water line.
Adding air with a bicycle pump or hand pump
A bicycle pump or hand pump works for small pressure increases — if your tank reads 20 PSI and you need 50 PSI, a hand pump will take a long time but will work. Unscrew the air valve cap and attach the pump nozzle to the valve stem. Make sure the connection is tight so air does not leak out around the sides.
Pump slowly and steadily. Stop every 10 to 15 strokes and check the pressure again with your gauge. This prevents you from overshooting the target pressure. Once you reach 40 to 60 PSI, remove the pump and screw the cap back on the valve.
Hand pumps are free if you already own one, but they are slow. Use this method only if your pressure is not far below the target or if you do not have access to an air compressor.
Using an air compressor for faster pressurization
An air compressor fills a tank much faster than a hand pump. You can rent one from a hardware store for $20 to $40 per day, or borrow one from a neighbor or friend. Plug it in, let it build up its own pressure (usually 90 to 120 PSI), and then attach the hose to your tank's air valve.
Turn on the compressor and watch your tank's pressure gauge. Air compressors deliver pressure quickly, so check the gauge every few seconds. Once you reach 50 to 60 PSI, turn off the compressor and disconnect the hose. Screw the cap back onto the air valve.
Do not exceed 60 PSI. Overpressurizing can damage the tank, the pressure relief valve, or the pipes connected to it. If you overshoot, open a tap in your house to release some water and pressure, then check the gauge again.
What to do if the tank keeps losing pressure
If you pressurize the tank and the pressure drops back to zero within a few days, the air valve is leaking. This is a sign the valve has failed and cannot hold air. You have two options: replace the air valve itself, or replace the entire tank.
Replacing the air valve requires draining the tank, unscrewing the old valve from the top, and screwing in a new one — a job that takes 30 minutes to an hour if you are comfortable with basic plumbing. A replacement valve costs $15 to $40. If you are not comfortable doing this, a plumber can do it for $100 to $200 in labor.
If the tank is more than 10 years old, replacing the whole tank may be cheaper than repairing it, because other parts are likely to fail soon. A new tank costs $300 to $800 installed, depending on size and type.
Dealing with a waterlogged tank
A waterlogged tank is completely full of water with no air pocket left inside. This happens when the air valve fails and air slowly leaks out over weeks or months, or when the pump runs continuously and fills the tank beyond its normal level. The tank will not hold pressure no matter how much air you add, because there is nowhere for the air to go.
To fix a waterlogged tank, you must drain it completely and let it refill. Turn off the pump, open the lowest tap in your house, and let water run until the tank is empty. Then turn the pump back on. As the tank refills, an air pocket will form at the top. Once the tank is full and the pump shuts off, check the pressure with your gauge. It should read between 40 and 60 PSI.
If the pressure is too low after refilling, add air using a pump or compressor as described above. If the tank becomes waterlogged again within a few weeks, the air valve is failing and needs to be replaced.
When to call a technician instead of doing it yourself
Call a plumber if the pressure gauge shows zero and stays at zero even after you add air — this usually means the gauge itself is broken or the valve is damaged beyond repair. Also call if you pressurize the tank, the pressure holds for a few days, but then drops again repeatedly. This pattern means the air valve is failing and needs professional replacement.
If your water pressure is still low after you pressurize the tank and the pressure holds steady, the problem is not the tank. It may be a clogged filter, a failing pump, or a blockage in your water line. A plumber can diagnose this with a pressure test at different points in your system.
Frequently Asked Questions
What PSI should my water tank be at?
Most household tanks should be between 40 and 60 PSI. Check your tank's label or manual for the exact range — some smaller tanks run at 30 to 50 PSI. If you are not sure, 50 PSI is a safe middle ground for most homes.
Can I use a car tire pump on my water tank?
Yes. A car tire pump works the same way as a bicycle pump and will pressurize a water tank. It will be slower than an air compressor but faster than a hand pump. Make sure the nozzle fits the air valve stem on your tank before you start.
How often do I need to pressurize my tank?
You should not need to pressurize a tank more than once every few years if it is working properly. If you find yourself pressurizing it every few months, the air valve is leaking and should be replaced. A failing valve will not hold pressure no matter how many times you refill it.
What happens if I pressurize the tank too much?
Overpressurizing can damage the tank, burst pipes, or cause the pressure relief valve to open and release water. If you go over 60 PSI, open a tap to release some water and pressure, then check the gauge again. Most tanks have a relief valve set to open at 80 PSI as a safety measure.
Do I need to turn off the pump before pressurizing?
Yes. Always turn off the pump before you pressurize the tank. If the pump is running, it will fight against the air you are adding and may damage the pump. Once you finish pressurizing, turn the pump back on and let it run normally.