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Get My Free PlanYour pool is only as clean as your filter is. The good news is that when you backwash, cleaning the filter doesn’t always entail taking it apart and washing it by hand.
Here’s a step-by-step guide on how to backwash a pool filter. You can watch the walkthrough video or keep reading for our complete guide.
An illustrated, step-by-step guide to taking care of your pool yourself. Works for chlorine and saltwater pools.
Whether you’ve heard the term “backwash a pool filter” or just “backwash a pool,” both are the process of reversing the flow of water in your filter to remove the buildup of contaminants.
As pool water passes through your D.E. filter or sand filter, it leaves behind dirt, oils, and other debris, which are collected in the filter medium—either D.E. powder or sand.
Over time, as water continues to pass in just one direction, the filter medium will become clogged, which will reduce your filter’s effectiveness. When you backwash a pool, you send water backward through the filter, and out the waste or drain port. This forces all the debris caught in the filter to dislodge so you can easily remove it and restore your filtration system to its normal functioning level.
While backwashing generally works the same way regardless of the type of pool filter, the procedures do vary a bit.
When you learn how to backwash a sand filter, the sand never leaves the filter. Water flows backward through the filter system and out through your filter’s waste port.
Before you get started, the only extra equipment you’ll need is a backwash hose.
When backwashing your pool filter, use this easy-to-roll up and store backwash hose.
Important: Never turn the multiport valve handle while the pool filter is on and running. This could cause the rubber diverter gasket inside the valve to come loose or break, which will cause water to leak out of the wrong ports while it’s running.
Before you get started, you’ll need a few supplies.
Filter media for backwashing and cleaning D.E. pool filters.
It’s a white powder composed of fossilized skeletons of one-celled organisms called diatoms. The powder is added to the filter and attaches itself to the grids inside, creating a D.E. “cake.”
This cake, along with the filter grids inside, helps to filter out very fine particles.
This will vary depending on the type and size of filter you have. Always refer to your owner’s manual for specific information.
In any case, D.E. powder is measured in pounds, so use a one-pound D.E. scoop to make measuring easy. In a pinch, you can also use an empty one-pound coffee can.
| DE Filter Sq. Ft. | One-Pound DE Scoop | One-Pound Coffee Can |
|---|---|---|
| 24 Sq. Ft. | 3 Pounds | 6 Cans |
| 36 Sq. Ft. | 4.5 Pounds | 9 Cans |
| 48 Sq. Ft. | 6 Pounds | 12 Cans |
| 60 Sq. Ft. | 7.5 Pounds | 15 Cans |
You’ll want to set aside a little time to do this, but don’t worry. It’s not an arduous task that’s going to take all day.
Important: Never turn the multiport valve handle while the pool filter is on and running. This could cause the rubber diverter gasket inside the valve to come loose or break, which will cause water to leak out of the wrong ports while it’s running.
This procedure differs only slightly from the multiport valve process.
When you first set up your filter, whether it’s sand or D.E., take note of the pressure gauge reading. That’s your normal operating filter pressure. Over time, as the filter starts to accumulate dirt and debris, pressure will begin to build up because the water can’t flow as freely through it.
When the pressure gauge reads 10 pounds per square inch (psi) above the normal operating level, it’s time to backwash. If it reads more than 10 psi over the normal level, it’s really time to backwash.
While you could backwash before the pressure reaches the 10 psi over the normal mark, we recommend waiting. Yes, your filter functions better when it’s not clogged. But before it gets to the fully clogged point, the presence of small dirt and debris actually helps your sand or D.E. filter work a little better.
Those tiny bits of debris help to catch and stop other tiny bits of debris from getting through the filter medium and making it back into the pool water.
So, a clean filter is good. A slightly dirty filter is better. A clogged filter is bad and needs to be backwashed.
Every time you backwash your pool filter, you could be pulling hundreds of gallons of water from your pool. Where is all that water going to go? Into your yard? The street? The creek behind your house?
None of those are good options, and in fact, may even be illegal, depending on where you live. The water that comes out of your pool is chemically treated and can damage plant life, groundwater, and aquatic life.
Disposing of backwash water properly is essential, not just to avoid potential fines, but to keep your community and the environment safe from illness and damage.
Some cities do allow pool water to be released into storm drains. But they may also require that you apply for a permit first.
You may also need to reduce or eliminate chemicals or salt levels in the water before you’re allowed to dispose of it in your community’s sewer system. Check with your local water authority.
You may be able to dispose of backwash water by directing it into one or more of your home’s plumbing cleanouts. Again, it’s best to check with your local water/sewer authority to ensure this is allowed, find out whether you need to treat the water in any way before disposing, and to obtain any necessary permits.
It’s unlikely any municipality will allow you to release pool water into a septic system. You wouldn’t want to do that anyway. Septic systems rely on the existence of active enzymes to dispose of waste. Pouring chemically treated water into the tank—especially water with chlorine in it—would likely kill those enzymes, leaving you with quite a mess.
These can be a life (or property) saver if you live in an area that sees a high level of rainfall, or experiences tropical storms. They can help prevent flooding and erosion. While a dry well could work for disposing of pool water, that’s not usually its purpose.
Regardless of how many levels of gravel, sand, or other media the water may pass through, it will still end up in the ground, which means it can be a problem if you live in an area that doesn’t allow the disposal of pool water into the ground.
Aside from the issue of permission, a dry well must be constructed by a professional, and it’s a project that can easily cost thousands of dollars.
You can definitely find an easier, safer, and less expensive way to dispose of your filter backwash water. Your local water authority can help you.
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Matt is the founder of Swim University. He's been in the pool and spa industry since 1996. His mission is to make pool and hot tub care easy. Each year, he continues to help people with water chemistry, cleaning, troubleshooting, and more.
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