clock menu more-arrow no yes mobile

All About Water Storage Tanks

Learn the differences between the common kinds of tanks found in home well-water systems, how they work, and what type you’ll need.

A water storage system outside a new home. iStock

An estimated 23 million homes in the United States get their drinking water from private wells, and most of those wells include one or more water storage tanks that may need to be repaired or even replaced at some point.

These tanks work with pumps, pressure gauges, and valves to maintain consistent water pressure, store water for immediate use, and increase the longevity of components in the home plumbing system. Read on to learn about the different types of well water tanks and to find out how to choose the right one for your home’s potable water supply system.

Pressure Tanks Manage Water Supply

Nearly all modern water wells include what is typically called a pressure tank. This is often a tall painted steel or fiberglass cylinder that sits between the pipe coming from the well pump and the rest of the home’s plumbing.

This tank has two main jobs: It ensures that there is sufficient but not excessive water pressure in your pipes, and it holds a reserve of water so that your well pump isn’t switching on and off every time there is demand for water somewhere in the system.

How a Well Tank Maintains Water Pressure

It takes pressure to deliver water to all your home’s fixtures and appliances. If there’s not enough pressure, appliances won’t work properly. That said, too much pressure could cause leaks and premature wear throughout the plumbing system. A well tank works in conjunction with a well pump, a pressure switch, and a check valve to keep the water pressure in a safe and comfortable range.

Inside the tank is a rubber bladder, similar to a tire innertube, which holds pressurized air to force the water out of the tank and into your pipes. A pressure switch on the tank tells the well pump to turn on when the tank pressure drops to the bottom of a satisfactory range–typically 30 or 40 pounds per square inch (psi). The switch turns the well pump off once the pressure reaches the top of the desired range, which is usually 50 or 60psi. A one-way check valve between the tank and the pump prevents the pressure from leaking back down into the well.

Choosing the Right Pressure Tank

The correct size tank is one that holds enough water in reserve to allow the well pump to run for a manufacturer-specified number of minutes each time it turns on in order to minimize wear and tear on the pump. If you are replacing a faulty tank, you may be able to just buy a tank that is the same size as the old one, but it’s safer to contact a tank distributor to help you choose the right one.

Pressure tanks are measured in water capacity–which can range from just a couple gallons to over a hundred. The ideal size tank for any plumbing system is based on what is called the drawdown rate, which is a function of the flow rate of the well pump, the pump’s minimum runtime, and the on and off settings of the tank pressure switch. Collect those numbers and then call a tank manufacturer’s tech support line to get help choosing.

Amtrol, one of the most well-known tank manufacturers, has an online calculator to make it even easier to find the right size tank. But if figuring all of this out on your own seems confusing or intimidating, it may be best to call a plumber for help.

Why Some Wells Have Additional Storage Tanks

The amount of water any well can provide in a day is limited by the flow capacity of the well itself. A slow-flowing well may work fine for some homes, but if you have a big family, a garden that needs frequent watering, or a hot tub that regularly needs topping off, an underperforming well may periodically run dry. When a well doesn’t keep up with a home’s demand, sometimes the owners may choose to drill a deeper well. But you can also add one or more storage tanks, which can often be a more affordable option.

How a Storage Tank Works

Non-pressurized storage tanks–also called cisterns–don’t replace the pressure tank in a well system. Instead, they get installed between the well pump and the pressure tank, providing a large reserve that the home can draw from when demand for water is high—without running the well dry.

In a pumped storage system, the well pump is controlled by a float valve in the storage tank rather than running off of a pressure switch. When the tank gets low, the valve will tell the pump to run continuously until the tank fills back up. The pump will also automatically turn off if the well runs dry, but under normal conditions that won’t impact the home’s water supply, as there will still be reserve supply in the tank.

As technology has improved, modern storage tanks, such as the Epp Well Solution System, have replaced the simple float valve with digital flow meters that constantly monitor the output of the well to more efficiently manage backup water supply.

Selecting the Right Size Storage Tank

How much capacity you need in a water storage system depends on how much water you will use at peak demand. For a small family, a 200-gallon storage tank may be plenty to supply several showers in the morning and the occasional high demands caused by holiday gatherings or filling a small bathtub.

If a house hosts large parties, has an oversized soaking tub, or supports a sizable vegetable garden, a bigger tank will be needed. Plus, a very slow-flowing well or one in a drought-prone region may need a tank that holds more than a day’s reserve. To get the right well water storage tank for you, you will need to do some homework to estimate your peak demand and the time it takes for your well to refill the storage tank. Tank distributors and manufacturers will have knowledgeable people on staff to help you figure this out.

Water storage tanks come in more shapes, sizes, and materials than pressure tanks, so it can be harder to decide which type to buy. Small plastic tanks might make the most sense if you need to install them in a basement with limited access. Some types of steel, plastic, and fiberglass tanks can be buried underground to save space. The factors that determine the ideal type of tank will vary by location, so it’s best to check with a local well system installer or your building department to make an informed decision.

Storage Tanks Don’t Replace Pressure Tanks

Because storage tanks do not pressurize water, a home with one of these tanks will still need a pressure tank. And because the primary well pump is filling the storage tanks and not directly feeding the pressure tank, an additional pressure pump is necessary between the storage and pressure tanks to actually provide the home’s water pressure. In other words, a storage system for a low-yielding well adds to the complexity and cost of the system–but if your well isn’t meeting your demands, it will likely be an essential expense.