If your pool water looks cloudy, the return jets feel weak, and the pressure gauge keeps climbing, your filter may be packed with dirt and debris. To backwash an inground pool, you reverse the water flow through a sand or DE filter to flush trapped dirt out through the waste line. Cartridge filters cannot be backwashed.
The key is knowing when to backwash and when to stop. Running the cycle too short may leave debris behind, while running it too long wastes water and lowers your pool level.
Before You Start: Can Your Pool Filter Be Backwashed?
Sand and DE filters can be backwashed. Cartridge filters cannot. Before you touch the multiport valve or start a backwash, make sure your filter is designed for it. Not every inground pool filter uses this cleaning method, and using the wrong procedure can damage the filter or reduce its performance.
The table below shows which filter types can be backwashed and how each one should be cleaned.
| Filter Type | Can You Backwash It? | How It Is Cleaned | Key Note |
|---|---|---|---|
| Sand filter | Yes | Backwash the filter, then run a short rinse cycle before returning to the Filter setting. | Backwash when the pressure gauge is 8 to 10 PSI above the clean starting pressure. |
| DE (Diatomaceous Earth) filter | Yes | Backwash the filter, rinse if your valve has a rinse setting, then recharge it with fresh DE powder. | Backwashing flushes out the old DE coating, so you must add fresh DE powder through the skimmer once the pump is running on the Filter setting. |
| Cartridge filter | No | Turn off the system, remove the cartridges, and clean them thoroughly with a garden hose. | Cartridge filters have no backwash setting, so rinse the cartridges by hand instead. |
| Some hybrid or brand-specific systems | Check the owner’s manual | Follow the cleaning method recommended by the manufacturer. | Valve labels and cleaning steps differ by brand, so the standard sand filter steps may not apply. |
If you are not sure which filter your pool has, check the label on the filter tank or look in your owner’s manual before getting started.
When Should You Backwash an Inground Pool?
Backwash your inground pool when the filter needs cleaning, not because a set number of days has passed. The pressure gauge tells you when. Backwash when the reading is 8 to 10 PSI above the clean filter pressure. Some manufacturers set a slightly different limit, so check your filter manual.
Clean filter pressure is the PSI reading right after a backwash and rinse, with the valve back on the Filter setting. If your gauge reads 14 PSI after cleaning, that is your baseline, and it is time to backwash at about 22 to 24 PSI. Write this number on the filter tank or keep a note at the equipment pad.
You may also need to backwash if the return jets feel weaker while the gauge reads high, or if the water turns cloudy and pressure is above baseline. If the flow is weak but the pressure is low, check the skimmer and pump baskets first. Vacuuming heavy debris through the filter, algae cleanup, storms, wind, and dust can also raise pressure faster.
Avoid backwashing just because it is on your maintenance calendar. A sand filter traps fine particles better with a little dirt buildup, so a slightly higher reading is normal. How often you backwash depends on debris, swimmer load, and algae, so let the gauge decide, not the calendar. It is one of the smaller jobs inside routine pool maintenance.
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What Do You Need Before Backwashing an Inground Pool?
Before you start backwashing your inground pool, make sure you have the right equipment and conditions ready. Setting up first helps you avoid mistakes once the pump is running.
You will need:
- A working pressure gauge to check your filter pressure before and after backwashing.
- A backwash hose or fixed waste line to safely direct dirty water away from the pool area.
- A safe drainage area where the discharged water will not damage your yard, landscaping, or nearby structures, and where local discharge rules allow it.
- Access to the multiport valve to switch between Filter, Backwash, and Rinse settings.
- A pool water level above the middle of the skimmer opening, so the pump does not draw in air while backwashing.
- DE powder, if you have a DE filter, because backwashing flushes out the DE coating and it must be replaced.
- Your owner’s manual if the valve labels or cleaning steps are different from standard settings.
How Do You Backwash an Inground Pool Sand Filter?
Backwashing a sand filter is simple, but the order matters. Always turn off the pump before changing the multiport valve setting, because moving the valve while the pump is running can damage the valve’s internal gasket.
1. Turn Off the Pump and Prepare the Backwash Setup
Start by turning off the pool pump completely. Never move the multiport valve while the pump is running.
Attach the backwash hose or prepare the fixed waste line. Make sure the discharge water flows away from the pool, home foundation, neighbors’ property, and sensitive landscaping.
2. Set the Valve to Backwash and Start the Pump
Move the multiport valve handle to the Backwash setting and make sure it locks into place.
Turn the pump on and watch the sight glass as dirty water leaves the filter. Continue backwashing until the water looks clear. This often takes 2 to 3 minutes, but a heavily dirty filter may need 3 to 5 minutes.
Stop once the water runs clear, since longer backwashing wastes water and can lower the pool level, and the refill is one of the pool costs owners forget to budget for. If your filter has no sight glass, backwash for about 2 to 3 minutes and confirm the result with the pressure gauge afterward.
3. Turn Off the Pump and Switch to Rinse
Turn the pump off before changing the valve setting. Move the valve handle to the Rinse position and make sure it locks into place. The rinse cycle resettles the sand bed and flushes leftover dirty water to waste, so it does not return to the pool.
4. Complete the Rinse Cycle and Return to the Filter Setting
Turn the pump on and run the rinse cycle for 30 to 60 seconds, or until the sight glass is clear. Turn the pump off again, move the valve back to the Filter setting, and lock it into place.
5. Restart the Pump and Check the Pressure
Turn the pump back on and check the pressure gauge. The reading should return close to your clean filter pressure baseline. If it stays high, see the troubleshooting section below.
If the pool water level dropped during backwashing, add water until it is back above the middle of the skimmer opening.
How Do You Backwash a DE Filter?
Backwashing a DE filter is similar to backwashing a sand filter, but it requires one extra step. After cleaning, you must add fresh DE powder to restore proper filtration.
- Turn the pump off before changing the multiport valve setting.
- Set the valve to Backwash and turn the pump on.
- Run the backwash cycle until the water looks clear, usually 2 to 3 minutes. Stop once it runs clear, since longer backwashing wastes water.
- Use the Rinse setting for about 30 to 60 seconds if your system has one, to flush leftover dirty water to waste.
- Turn the pump off, return the valve to Filter, and restart the pump.
- With the pump running on the Filter setting, add the correct amount of DE powder through the skimmer to recharge the filter. Wear a dust mask when handling the powder.
- Check the pressure gauge once the DE has circulated, and note that reading as your new clean pressure baseline.
- Check the manufacturer’s instructions because DE filter designs and DE requirements can vary by model.
Do not run a DE filter after backwashing without adding fresh DE powder. Without the DE coating, the filter does not trap fine particles well, and dirt and oils can clog the grids and shorten their life.
DE backwash water is often restricted more tightly than sand backwash water. Many cities don’t allow it near the street, storm drain, or a neighbor’s property, so check your city’s rules before you discharge it.
What Backwashing Mistakes Should You Avoid?
Backwashing is a simple maintenance task, but small mistakes can damage your pool equipment or reduce filtration performance. Avoid these common problems:
- Moving the valve while the pump is running: Always turn off the pump before changing the multiport valve setting, as pressure can damage the valve’s internal gasket.
- Skipping the rinse cycle: Rinsing resettles the sand bed and flushes leftover dirty water to waste, so it does not return to the pool.
- Backwashing a cartridge filter: Cartridge filters have no backwash setting, so remove the cartridges and hose them clean instead.
- Backwashing too often or too long: Extra backwashing wastes water and can reduce the filter’s ability to trap fine particles, so stop once the water runs clear.
- Letting the pool water drop below the middle of the skimmer opening: Low water lets the pump pull in air and lose prime, which can damage it.
- Draining water into a bad location: Direct backwash water away from your home, pool, neighbors, and sensitive landscaping, and follow local discharge rules.
- Ignoring a broken pressure gauge: A faulty gauge hides when your filter needs cleaning and whether backwashing actually worked.
- Assuming backwashing fixes old sand or damaged laterals: Backwashing cannot repair worn sand or broken laterals, the internal pipes that collect filtered water.
- Forgetting DE recharge after a DE filter backwash: Add fresh DE powder through the skimmer once the pump is running on Filter to restore proper filtration.
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What If Pressure Is Still High After Backwashing?
If pressure stays high after backwashing, something is restricting flow at or after the filter. Check these first:
- A partly closed return valve or a blocked return line
- A multiport valve that is damaged or not fully locked on Filter
- A faulty gauge, which you can rule out by comparing it with a second one
- Old or clumped sand, which typically needs replacing every 3 to 7 years
- A filter that is too small for the pool
Algae and fine debris can reload the filter quickly, so clear green or cloudy water before judging the result. Sand in the pool points to broken laterals, the internal pipes that collect filtered water. Weak flow with low pressure is a different problem, so check the skimmer and pump baskets.
If pressure stays high after a full backwash, don’t keep repeating it, since that wastes water and lowers the pool level. Call a pool professional if you can’t find the cause.
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FAQs
Where can you drain pool backwash water?
It depends on your city, so check local rules before you backwash. Most cities don’t allow backwash water in the street or storm drain. Common allowed options are your own landscaping, as long as nothing runs onto a neighbor’s property or the street, or your home’s sanitary sewer cleanout. Never use a sewer manhole in the street. In Phoenix-area cities such as Mesa, for example, the street and storm drain are off limits, and no permit is needed to use your own cleanout.
Can I backwash during water restrictions?
Check your city’s current drought stage first, since every backwash means topping off afterward. Many cities limit filling pools or restrict it to protecting equipment. Backwash only when the gauge calls for it, and ask your water provider whether topping off is allowed right now.
Do you backwash a pool before or after you shock it?
Backwash before shocking only if the pressure is already 8 to 10 PSI above baseline. Then shock the pool and run the pump so the filter can catch dead algae and contaminants. Check the gauge afterward, and backwash again if pressure rises, since dead algae can load the filter quickly.
What does the air relief valve do?
It lets trapped air out of the filter. When you restart the pump after backwashing, open the relief valve and close it once water flows steadily from it. Trapped air can build pressure in the tank, so follow your filter’s manual.
Why is dirty water coming back into my pool after backwashing?
Usually the rinse was skipped, the valve isn’t fully locked on Filter, or a worn multiport gasket lets water bypass. Sand in the pool points to broken laterals instead. Run a full rinse and check the valve; if it keeps happening, have the valve or laterals inspected.
How much water do you lose when backwashing a pool?
Roughly 150 to 400 gallons for a typical backwash and rinse, depending on pump flow and cycle length. How far the level drops depends on your pool’s size. As a rule of thumb, one inch of water equals about 0.62 gallons per square foot of surface. Refill to mid-skimmer before you walk away.
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