A water storage tank holds clean water from your reverse osmosis system or other filter systems until you're ready to use it. Pressurized storage tanks force water out on demand, while atmospheric tanks require a booster pump to supply pressure. Here's what John Woodard, our Master Water Specialist, says about how a water storage tank works and what it's used for. 

What is a water storage tank?

A water storage tank stores water for use later. They're used for low-recovery or low-pressure well systems where water has to be pulled from the well to run through the household. Reverse osmosis (RO) systems also use a storage tank. Water storage tanks used in the water treatment business come in all sizes, shapes, and configurations.

How does a water storage tank work?

A water storage tank simply holds water until we need it. A pressurized storage tank has the ability to force water out. That's what the pressurized side of that tank is for. An atmospheric tank holds water until it's drawn out with a booster pump.

water storage tank

What are water storage tanks used for?

An RO storage tank works through a slow process. Water accumulates in a storage tank until you need it and can use it. A point-of-use (POU) reverse osmosis system is usually coupled with a three-gallon storage tank that's hydro-pneumatic with a pressure system or a pressurized chamber inside to push water out. If the RO storage tank is used on a larger scale, like treating water for the whole house, it's stored after reverse osmosis filtration and pumped through the house when needed. There's a variety of applications for big and small water storage tanks.

How do you install a water storage tank?

well storage tank install kit

It depends on how the storage tank is going to be used. The small, pressurized tank used for reverse osmosis just connects with a piece of tubing. If you're setting up a well system, the pressure tank should be installed with:

  • Water inlet from the well
  • A check valve
  • A pressure relief valve
  • A boiler drain to drain the tank down if needed
  • A pressure switch to tell the well pump to turn on and turn off based upon how much water and pressure builds in the tank

| Learn how to size your well pressure tank. |

Why are water storage tanks elevated?

Storage tanks that are elevated are typically atmospheric, like the big water tower tank in your community. The water is pumped up into the tank and held. When you open the tap at your house, the column of water on the way up to the tower creates water pressure to deliver water all the way to your house. Some storage tanks for water at your house are elevated to add pressure to force water out.

How do you keep a water storage tank from freezing?

Don't put it in a place with freezing temperatures. A frozen tank is a concern if you live in a cold part of the country and have to have a storage tank outside. Take measures to keep water moving so it doesn't have a chance to freeze, like installing an aeration pump. Most of the time, you can install a storage tank in your house or barn to keep the water from freezing.

How do you keep storage tanks clean?

It depends on the style of tank. If you're using an atmospheric tank, you're probably going to put a couple of drops of chlorine in it every so often. Depending on the size of the tank, you may need a couple of cups of chlorine. On a reverse osmosis or pressurized storage tank, run sanitizing solution through it periodically because there's a chance that slime can accumulate in the tank. On all water storage tanks, it's a good idea to drain them down, put sanitizing solution in, and flush the tank. Your tank could require cleaning semiannually or annually depending on the quality of water going into the tank. 

How do you know what size water storage tank you need?

The size of the water storage tank depends on the application and what your usage patterns are. If you're sizing a reverse osmosis system for drinking water for a large house or maybe even a small office, estimate how much demand will be on that system and size accordingly based on RO output and storage. If you're using the tank in an office with high water demand, draw a lot of water first thing to make coffee and around lunchtime for people getting water. You'll need enough water storage to meet the high demand. For a household, there's a formula based on the size of your pump and how long it needs to run in a cycle. If you need to size an atmospheric tank, you'll need to know your water demand. If I'm using the water for irrigation or to run a household, then I want to size large enough to cover my demand for a day.

How do you calculate water storage tank capacity?

Capacity for a storage tank or reverse osmosis storage tank is based on demand, or how much water we're going to drink or cook with or use in the break room. If you need a tank for a restaurant with a coffee brewer or other beverage and food equipment, the size still depends on how much water you need and how much the tank can hold.

What is an underground water storage tank?

An underground water tank is typically called a cistern. It can be up to thousands of gallons in size. Outside of the United States, many homes store water in a cistern. Water pumps up into this cistern up on the roof of a house and provides all the water you get for the day. Underground water storage tanks hold a couple hundred to a couple thousand gallons and can be used for rain harvesting throughout a household.


  • Hi Kim,

    Pressurized or hydro-pneumatic storage tanks work on the same physics no matter if for a well application or use with a reverse osmosis system. But they do work at different precharge pressures. A well tank could be used as a storage tank for a reverse osmosis system by adjusting the empty tank precharge. However, the RO tanks are typically lined so the high purity water is protected.

    John Woodard, Master Water Specialist on

  • Could you use a water well tank on an osmosis system?

    Kim on

  • Hi Vivek,

    We would love to help. If you can take a few pictures of the system and the way it is installed to, we will try to help solve the problem.

    Filter cartridges in an active system will always have water in them. That’s normal and causes no issue.

    John Woodard, Master Water Specialist on

  • I have a 5 stage RO system at home, unfortunately the storage tank was not installed properly and instead the mains water runs straight into the filters and out the filter faucet. Is there a hygiene issue with water constantly being in the filters rather than in a storage tank?

    Vivek Sreenivasan on

  • Hi Michael,

    What size tank is it? Is it used on an RO system? It sounds like your tank has lost the air charge that forces the water out of the tank. The first step is to drain all the water out of the tank. You may have to add a small amount of air through the schrader valve on the tank. A small compressor or a bicycle pump can be used for this. Be careful not to add too much air. A small amount (1 to 2 psi) is sufficient to force the water out of the tank.

    Once the tank is empty, use a tire pressure gauge to measure the amount of air pressure in the tank. RO storage tanks should have 7 to 8 psi for an air charge. Use the air pump to add enough air to bring it to this level. If the tank is used on a well pump system, a much higher air charge is required. The air pressure should be at 2 psi below the level that the pressure switch activates the well pump. For example, if the switch starts the pump at 30 psi, the air charge should be at 28 psi. Hope this helps. Please let us know if you have more questions.

    John Woodard, Master Water Specialist on

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