How do You Backwash an Inground Pool

If you have been an inground pool owner for some time, you already know that there are different maintenance requirements to keep the pool functional and clean. From maintaining the chemistry of the water, vacuuming, to regularly purchasing Unicel pool filter cartridge replacements, there are a lot of things to take care of.

One of the most popular ways for keeping the filter system of an inground pool working in the best possible way is backwashing. It is the process of reversing the water flow through your filter system to eliminate the build-up of contaminants.

Backwashing DE or Sand Filter Systems

With time, the media in your pool filter system can get too soiled and will not able to keep the pool as clean as it should. While the skimmer basket holds on to the larger contaminants, smaller particles like dirt, bugs, etc. pass through the basket.  Backwashing will clean the dirty filter media.

Regular backwashing is only required by sand and DE Pool Filters to ensure that they do not get clogged, a condition which can reduce the pressure of the filter and also inhibit water and chemical circulation in the pool. But note that backwashing is only a temporary solution for DE filters in cases where you cannot entirely clean the filter.

If you do not want to get into the regular maintenance requirement of DE and sand filter systems, you can select a cartridge filter system over them. These types of systems are easy to clean, are available in a number of choices, and it is fairly easy to find Unicel or Filbur pool filter cartridge replacements for any cartridge size.

Also, if you are planning to buy DE or sand filter, note that some municipalities prohibit their use due to water waste.  Make sure that you check with the local authorities if there are any such restrictions in your area.

Steps to Backwash a DE or Sand Filter System

Check the skimmer opening and make sure that the water in the pool is at least halfway up the opening. If not, add more water to the pool. Next, turn off the pool heater (if applicable) and wait approximately 15-20 minutes for the water to cool down.

Your filter system will have a drain valve which you need to open before closing the pump’s skimmer valve. Once the water is cool, you can then proceed to turn off the pump.

Close the drain valve that you opened previously and manually remove the pump basket along with the debris if any.

You might also have a backwash hose that you need to connect to the pump and move the other end away from the pool. This is where the waste water will flow from, so place it in a spot that is away from the pool, but will not cause flooding or damage. Once the hose is connected, you can turn the lever of your pump to the “backwash” position. At the top of your pump filter, there will be an air relief valve. Open it after turning the pump lever.

Now, turn on the pump and open its drain valve. Once the water starts to flow, skimmer valve should also be opened to quickly remove more water. If the water flow is good, you can again close the pumps air relief valve.

Run the pump for about 8-10 minutes. Check the sighting glass after this duration to see if the water flows clear. If it is clear, turn the pump off and turn the pump’s lever to the “rinse” position. Turn on the pump again and let it run for a minute before shutting it again.

Move the pump lever to the “filter” position.

Use a pool test kit to check whether or not the chemical composition of the water is as required. If not, make the required changes.

Turn on the water heater (if applicable) and you are ready to use the pool again.

How often is Backwashing Required?

There is no fixed time interval for backwashing. It depends on how often you use the pool and how dirty it gets with each use. A popular time to backwash used is when the pressure gauge shows a pressure increase of about 8-10 PSI above the normal starting pressure. The base starting pressure can be determined by noting what the pressure gauge shows just after a backwash. You should also backwash if there has been a major outbreak of algae in your pool or if your region has suffered from a weather event or storm and your pool is excessively dirty.

A good schedule is bi-monthly for DE filter systems and monthly for sand filter systems. DE filter system cartridges (or grids) should also be regularly cleaned and replaced.


Backwashing your inground pool filter system is a routine maintenance process which is very important for the functionality and health of your pool and its filter system. While you can also hire professionals for this job, you too can master it easily and manage it on your own.

Simply follow the steps listed above along with other basic maintenance routines to ensure that the pool filter system continues to function flawlessly.