How to backwash your pool – a step-by-step guide

backwash swimming pool
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As part of you ongoing swimming pool maintenance you will need to backwash your swimming pool filter. 

It’s one of the things we do when we are carrying out swimming pool maintenance. But it’s also something that you can do on your own if you know how. 

What is 'backwashing' a swimming pool filter

swimming pool sand filter

Ew! Backwashing. It doesn’t sound all that pleasant does it?

But backwashing is what we call it when you reverse the the flow of water through the filter. Instead of the water flowing through the filter and into the swimming pool (to clean the water). It flows from the swimming pool, through the filter and out a waste pipe. It is effectively cleaning and resetting the swimming pool filter to flush out any debris that has accumulated.

Sand filters need to be backwashed more often. However, glass and OC-1 filters also need to be backwashed.

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Why do I need to backwash my swimming pool filter?

To understand why you need to backwash filters, you firstly need to understand how a sand filter work. 

Sand filters work by a process of ‘entrapment’. Dirt and debris from the pool are trapped in amongst the sand grains. They then become part of the filter. This build up increases efficiency to a point. 

However, over time, this accumulation causes a build up in pressure. And because of the consistency of sand it can lead to ‘clogging’, creating channels for water to pass through unfiltered. If this pressure build-up is not relieved the filter will become less effective. And collected dirt will end up back in the pool. Leading to unclean, unsafe and cloudy swimming water. 

Periodically backwashing the swimming pool filter dislodges these contaminants and disposes of them through a waste pipe. 

This increases filtration efficiency. And leads to a cleaner, safer swimming pool. 

How often should I backwash my swimming pool filter?

In normal circumstances, it is recommended that you backwash your swimming pool filter once weekly. Ideally during the regular swimming pool service, after the pool has been vacuumed and cleaned.

An indicator that your swimming pool filter may need backwashing is when the pressure rises approx. 8-10psi above normal operating pressure (you can determine base pressure after a backwash and work from this).

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How to backwash a swimming pool filter: step by step guide

Step 1: 

Firstly, turn the pump off. This makes the system safe to work on and avoids damage. Work should never be carried out with the pump on.

Your pool will likely have a multi-port with six different settings (filter, backwash, rinse, circulate, closed and waste).

Alternatively, it may have a ‘pull/push’ handle – in one position the water will flow normally through the filter. In the opposite, it will flow through the backwash hose.

Steph 2: 

Next, make sure all the valves in the backwash line are open

Step 3: 

Then, turn the multi-port to ‘backwash’ – or turn the push/pull valve 180 degrees.

Step 4: 

Turn on the pump. You will see water flow through the backwash hose.

Continue running this until the water visible in the side glass runs clear. Typically takes 4-7 minutes.

Step 5: 

Then, turn off the pump.

Step 6:  

Turn the multiport to ‘rinse’ (if you are using a multi-port – if not skip to step 9).

Step 7: 

Next, turn on the pump and rinse (between 15-30 secs).

Step 8: 

Turn the pump off.

Step 9: 

Move all valves back to their original position. Move the multi-port back to ‘filter’ or turn the pull/push handle back around 180 degrees.

Step 10: 

Finally, turn the pump back on and water should flow back towards the pool as normal. 

Step 11:

Top the pool water back up if necessary

The benefit of backwashing less

As I said, you will need to backwash weekly, or if the pressure gets too high to improve the efficiency of swimming pool filtration.

But ideally, the less time you can backwash for the better. Backwashing pulls water out the swimming pool. This will then need to be topped up and reheated. So the more water is used during backwashing – the more energy and money is used to run the swimming pool.

This is why OC-1 and glass filter media is gaining popularity over traditional sand filtration. They require less frequent backwashing, for less time. And therefore cause the swimming pool to lose less water.

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In summary

Backwashing is a necessary part of swimming pool maintenance. 

Hopefully that has helped you understand how to do it yourself, or potentially why you need professional help.

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Debbie Ekins
Debbie Ekins
Eagle Leisure - Sales & Marketing Manager Mission = to arm you with the knowledge you need to make the best buying decisions. Fuelled by coffee (and naps). Explorer of Scotland and the world.
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