What’s Whole House Water Filter Backwash?

Author: Rory Mullan - Published: 2021/09/03 - Updated: 2023/01/05

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Whole house water filters with backwash are a blessing indeed! They not only filter water but also get rid of the contaminants accumulating in the filter media. That, essentially, prolongs their life and allows them to function effectively for a long time.

Since whole house water filters deal with a wide range of contaminants, backwashing serves a very important purpose.

In this article, we’ll cover all the details about backwashing water filters, including how they work and why you may need one in the first place.

So, here is our guide on whole house water filter backwash!


  • Backwashing filter systems clean your home’s water supply just like any other whole house water filter.
  • Filters for backwashing operate in two stages:
    • Phase 1: Filtration – Water is passed through filter media. Contaminants are trapped.
    • Phase 2: Backwash – Water is pumped through the tank in the opposite direction (backflushing). This causes the filter medium to expand and dislodges accumulated dirt to flush them down the drain. This then leaves the media clean and prepared to filter more water.
  • Ineffective backwashing usually causes the malfunctioning of water filtration systems.

How Does Whole House Water Filter Backwash Work?

Whole House Water Filter Backwash Thumbnail

In terms of appearance, a backwashing water filter looks pretty similar to a water softener. However, it doesn’t really soften the water. Its purpose is filtration only, whereas water softeners work to purify water and remove hardness.

Whole house backwashing water filtration systems work in two phases: filtration and backwashing. Let’s look at each in detail:

Filtration Phase

Backwash filters are tank-based filter systems. They feature a large tank, sometimes called a mineral tank, containing a filter medium.

The water enters the tank from the top (control valve). As it flows down, the filter traps the contaminants.

The exact methodology of trapping varies by the filter media and the contaminants in question. For instance, a filter may eliminate chlorine, chloramines and pesticides. Another unit may be used to filter sulfur and iron.

After passing through the filter media, pure water flows out the tank and into the plumbing of your home.

Backwash Phase

The backwash phase can be set up manually or automatically. It’s a periodic cycle where the water moves in reverse direction. This process is termed backflushing.

During this reverse flow of water, the filter media expands and releases the contaminants it has previously trapped. Now, the contaminated water is expelled via a drain, making the filter media clean again.

The backflushing cycle lasts for a set period, usually around 10 minutes, during which no filtration takes place. After that, the water flow returns to normal, with incoming water from the city or well going through the filter media in the tank. In some whole house filter models, the filter media is repacked with the help of a quick rinse.

Why Use Backwashing Whole House Water Filters?

Water filters, regardless of the type or quality, cannot last forever. Over time, they get packed with contaminants that reduce their ability to catch and trap more contaminants.

Backwashing or not, any system fails eventually and requires new filter media or replacement filter cartridges. However, you can prolong a filter’s service life considerably through backwashing.

How long a filter will last also depends on the quality of water, as heavily contaminated H2O will take a toll on the filter elements. They will clog or foul much faster if the water is overly dirty.

Sometimes large particles can also form a layer on top of the filter bed. This is called a filter cake. A filter cake can aid the filtration process blocking contaminants from reaching the filter media. However, when the layer gets too thick it can reduce water pressure noticeably. This ultimately beats the very purpose of installing a whole house water filter in the first place.

Backwashing deals with all these problems by clearing the filter media bed. Here’s how it benefits you:

  • It maintains the water pressure and flow in your home.
  • It renews the filtration capacity and ability of the filter media by removing impurities.
  • It increases the reabsorption capability of the filter through aeration.
  • It prevents a buildup of germs like bacteria and mold inside the mineral tank, keeping the system pathogen-free.

trickling faucet

How Often Should Filters in a Whole House Water Filter System Be Backwashed?

Now that you understand how exactly backwashing works and what benefits it brings, let’s discuss how often it should be used since this has a major impact on the life and performance of a filter.

There are three main aspects to consider:

  1. The type of backwashing whole house water filter
  2. Your water quality
  3. Your water usage

In most cases, a filter system will be programmed to backwash automatically, so you won’t have to worry about how many times the cycle needs to take place. However, even if it’s not automatically set, you can refer to the user manual for recommendations from the manufacturer.

For example, an iron filter certainly requires backwashing more frequently than a carbon filter:

An iron filter removing 13 ppm of both ferric and ferrous iron may require backwashing every few days. In comparison, a carbon filter may not necessarily need backwashing more than once a week or fortnight.

Pressure gauges can also help determine when it’s time to do a backwash cycle. Installing pressure gauges at both the entry and exit point can help you detect drops in water pressure. If the pressure drop exceeds 16 psi, which is generally the limit in whole house filters, it’s time to backwash.

You can manually start the backwash cycle by pressing the according button on your system. Make sure the valve is in the correct position. For exact steps, consult the user manual.

What are the Different Types of Backwashing Whole House Filters?

There are two types of impurities in your water:

  • Dissolved impurities: These cannot be seen, for example, dissolved metals, minerals, or salts.
  • Floating impurities: These can be visible in the water and may alter its appearance, for example sand.

There are backwashing filters for both categories. Let’s list them down!

Backwash Filters for Floating Contaminants

Here are the common backwash filter media types that help deal with floating contaminants in water:

Filter AG

Filter AG is perhaps the most commonly used in sediment filters designed for whole house applications. It’s also the most cost-effective method of getting rid of sand, silt and debris floating in water.

Micro Z

A Micro Z filter can trap sediment as small as 2 microns and as big as 20 microns. For this reason, it has great filtration capacity and generally lasts a long time.

It can also target specific pollutants in the water by customizing the zeolite grains.


This is a multi-purpose filter medium that not only deals with large sediment particles but also smaller particulates. It can eliminate oxidized iron, sand, marine sediments and other solid impurities.

Also, anthracite allows for higher flow and causes a lower pressure drop compared to some of the other sediment filter media.

water softeners and whole house water filters

Backwash Filter Media for Dissolved Contaminants

Filter media for dissolved contaminants utilize different processes such as absorption, adsorption and oxidation.

The different between absorption and adsorption? Absorptive filters absorb the contaminants inside them, similar to a sponge that absorbs water. On the other hand, adsorptive media attracts the contaminants to its surface like a magnet.

Here are several examples of backwashing filter media removing dissolved contaminants:

Activated Carbon

Granular activated carbon or GAC is one of the most common filter media in backwashing whole house water filters. It removes chemical contaminants such as chlorine, pesticides and herbicides.[1]

It also deals with aesthetic water issues like bad taste and odor by adsorbing the chemicals causing these issues.

Catalytic Carbon

Think of catalytic carbon filter media as GAC 2.0, as it’s designed for eliminating harder-to-remove contaminants like chloramines and hydrogen sulfide. While being super-efficient as a backwashing medium, it’s also more expensive.

Bone Char

Bone char is made by charring animal bones. The result is a porous material that has carbon, tricalcium phosphate, and calcium carbonate in its composition.

It is useful for removing fluoride, a halogen, from water. For a very long time now, city water has been fortified with fluoride as it can help avoid tooth decay. However, excessive fluoride consumption can cause fluorosis[2], which involves tooth and bone damage.

The tricalcium phosphate in bone char removes the fluoride.


Birm is an absorbent medium that targets iron in particular. It contains aluminum silicate and manganese salt. However, it only works for water with a pH of 6.7 or higher. If the water is too acidic (lower than 6.7 pH), Birm will not work as effectively as one would like for iron removal.


Greensand is a useful filter media for eliminating iron, hydrogen sulfide and manganese.

It’s basically a siliceous mineral combined with manganese oxide. During the regeneration cycle, potassium permanganate activates and clears the surface.

pH Neutralizer

If your water is acidic, a pH neutralizing filter can balance pH levels. Most commonly, these types of whole house water filters use calcium carbonate (calcite) to counter the acidity of water and make it more alkaline or near neutral.

Backwashing: Pros and Cons

Let’s round up the advantages and disadvantages of backwashing whole house water filters.


  • Backwashing increases the life of the filter media.
  • There are many different types of backwashing filters, allowing you to customize the setup for your particular water problems.
  • Their installation is easy.
  • No bacteria or mold grows inside the system.
  • No pressure loss or media channeling.
  • EBCT leaking can be prevented.


  • It’s dependant on electrical power to function.
  • Some water goes to waste, but it can be repurposed (e.g. irrigation use).
  • Smaller empty bed contact times, but that can be addressed with a larger tank size.

Poor quality or design of the filter can negatively impact the mass transfer zone.


In conclusion, whole house water filter backwash kicks in when a system has processed a certain amount of water and accumulated a certain amount of contaminants in its filter media bed.

During backwash, the water flow is reversed to expand the bed and flush all dirt down the drain.

This prolongs the filtration capacity and therefore life of the filter media by a great bit. To be more precise, backwashing water filters can last for more than 10 years.

Other benefits are steady water pressure and flow around the house, control of pathogenic growth, no media channeling and prevention of EBTC leakage.

How often a whole house filter needs to backwash depends on its type, your water quality and your water usage.

Commonly used backwashing filters for floating contaminants are Filter AG, anthracite and Micro Z.

Activated and catalytic carbon, greensand, Birm and calcite are often used to remove dissolved contaminants.

The main disadvantages associated with whole house water filter backwash are wastewater production and smaller empty bed contact times.

Further Reading


Meet Rory Mullan

Rory Mullan Rory has joined the Water Masterz team as a contributing writer. He has covered all sorts of topics in the last several years.

Outside of his writing work, Rory enjoys photographing the Irish landscape and making music!

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