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How Does a Dual Tank Water Softener Work?

Scott Winfield
Written by Scott Winfield
Last Updated on

This guide breaks down the science behind dual-tank water softeners and explains their benefits over standard water softeners. If you’re on the fence regarding dual tank models and standard water softeners, we’ll help you understand what would be a better choice for you.

Dual Tank Water Softener

Let’s start with the main thing that distinguishes dual tanks from traditional water softeners: the number of tanks.

How Are Dual Tank Water Softeners Different Than Standard Water Softeners?

Dual tank water softeners are an upgrade of single tank, or traditional, water softeners. They were designed for households in need of continuous water softening without interruptions.

Dual-tank and single-tank water softeners differ in several ways.

Dual tank models:

  • use two resin tanks
  • deliver soft water without interruption
  • require a special control head that connects the two tanks
  • require a bit more room to install
  • cost more money

Dual tank systems use two resin tanks but only a single brine tank for the regeneration process. Because of this, the two resin tanks alternate in operation, ensuring that you always have soft water available. Traditional water softeners have a single tank that needs to regenerate periodically, which means that you may not have access to soft water during the regeneration cycle. This is an inconvenience that dual tanks successfully overcome.

The resin tanks are identical, so the control head, or the brain, can be installed on both. However, instead of a single bottom connection, the brain has a double connection at the bottom so that both resin tanks can be attached.

Aside from that, the only difference between the two water softener models is the required space. You’ll need more room in your basement to fit the second resin tank. However, since these tanks are usually around 10” to 15” wide, it shouldn’t be that much of an issue for most households.

Finally, buying a unit with two resin tanks will cost more than a standard unit. You should expect a price difference between $300 and $600 between single and double models. Keep in mind that the price may increase depending on the model and the quality of the water softener itself.

How Do Dual Tank Water Softeners Work?

Installing dual tank softeners

Installing dual tank softeners works similarly to how you would install a single tank system, so we won’t go too far into detail here, but you should check some of our articles on the topic if you’re interested.

The main point you need to know is that the water pipes and the brine tank lines are connected to input and output valves on the control head at the top of the resin tanks.

Once the setup is done and the softener is turned on, the brain will start funneling water into the resin tanks like normal. However, the resin tanks don’t work simultaneously, and water will only flow into one at a time.

When the first resin tank has softened a certain amount of water, the timed regeneration cycle should kick in and replenish the sodium supply that was depleted due to the ion exchange process.

While one tank regenerates, the water will be redirected into the second resin tank. Even if the regeneration process stops in the first tank, the water will keep being directed into the second tank until the beads need to be regenerated.

The regeneration process then starts in the second tank, and water is redirected to the first tank.

Since one tank will always be able to soften the water, there’s no downtime while you’re waiting for the regeneration cycle to finish. Where single tank units would be out of commission for 30 minutes to 2 hours, dual tank units never need to stop softening the water.

Advantages of Dual Tank Water Softeners

The most significant advantage of dual tank systems over standard water softeners is that they soften water continuously, without interruptions. If one tank is undergoing a regeneration cycle, the second tank will cover the filtration process until the cycle ends. This is useful in large buildings with many homes since it means all tenants will have access to soft water at any time of the day or night.

Moreover, dual tank water softeners typically have a higher water flow rate than traditional units. As a result, you can run more appliances and fixtures simultaneously without a water pressure or flow drop.

Dual tank water softeners also feature a “counter-current regeneration,” which uses less salt and water than traditional water softeners. This makes them more environmentally friendly and cost-effective in the long run.

Finally, since the tanks are also used interchangeably, the resin in each tank is used half as much as it would be if you were using a single-tank system. So, the resin will last far longer than on standard systems if you use them in the same environment.

Disadvantages of Dual Tank Water Softeners

As you might expect, buying a second tank is expensive, so the initial purchase price of these systems is higher than standard water softeners.

Furthermore, dual tank models require more complex installation and plumbing, which increases the installation cost and time. You may need to hire a professional plumber to install the system correctly.

Dual tanks also take up a bit more space in the room where they’re installed. As mentioned, resin tanks are generally tall but not very wide, so placing them is not difficult. However, you still need to plan out the space in advance to ensure you can accommodate the extra resin tank.

Finally, these models require more maintenance than traditional water softeners. You’ll need to monitor both tanks and ensure the system is operating correctly to avoid downtime.


In conclusion, the addition of the second tank in dual tank models allows for an interrupted water softening process. These models work similarly to traditional water softeners, with an alternating scheme between the two tanks. What this means is that when one tank regenerates, the other one takes over. In all other aspects, they work just as regular water softeners.

Dual tanks are invaluable for large households or apartment buildings but are too powerful for most other applications.

We highly recommend getting a dual tank system rather than a more powerful softener or two water softeners if you need an uninterrupted water flow.

In any other situation, we recommend sticking to a standard model.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
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