How to Backwash a Pool Sand Filter: Steps, Litres and Cost

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How do I backwash my sand filter? Turn the pump off, set the multiport valve to BACKWASH, run the pump 2–3 minutes until the sight glass runs clear, then RINSE about 1 minute and return to FILTER, one media filter maker says. Backwash at 40–50 kPa above clean. At 173 L/min, 3 minutes plus the rinse is 692 litres, $2.36 in Sydney.

The short answer

When: one media filter maker says backwash when the gauge reads 40–50 kPa above the clean reading; a 22-inch sand filter maker says 50 kPa and at least once a month.
How long: backwash 2–3 minutes or until the sight glass runs clear, rinse about one minute (one maker); 15–30 seconds of rinse (another); rinse about half the backwash time (a third).
The litres: flow × minutes. 173 L/min for 2 minutes plus a 1 minute rinse is 519 L; 3 + 1 minutes is 692 L; a council guideline’s 400 L/min for 3 minutes is 1,200 L.
The cost: 692 L is $2.36 at Sydney Water’s $3.41/kL, $2.65 at Yarra Valley Water’s $3.8313 and $1.46–$1.94 at Perth’s first two tiers. Monthly, that is 8.3 kL and $28.32 a year in Sydney.
Never turn the valve with the pump running, and never backwash in rain where your utility forbids it; Hunter Water does.

The backwash ledger: litres sent to waste by one backwash and rinse at five stated flows, and the water cost at 2026–27 usage prices (Sydney Water $3.41/kL; Yarra Valley Water step 1 water and sewer usage $3.8313/kL; Water Corporation Perth tier 1 $2.108 and tier 2 $2.809/kL). Flows and times from two filter makers’ manuals, one pump maker’s turnover table and a Fraser Coast council guideline (vendor-published figures labelled). Our arithmetic, read 22 October 2026
Scenario	Flow	Backwash + rinse	Litres	Sydney	Melbourne (YVW)	Perth tier 1 / tier 2
One maker’s 25-inch-class media filter, minimum backwash flow	173 L/min	2 min + 1 min	519 L	$1.77	$1.99	$1.09 / $1.46
The same filter, a longer backwash	173 L/min	3 min + 1 min	692 L	$2.36	$2.65	$1.46 / $1.94
One 22-inch sand filter at its maximum flow	228 L/min	3 min + 30 s	798 L	$2.72	$3.06	$1.68 / $2.24
One pump maker’s high speed (50,000 L in 3.3 hours)	253 L/min	3 min + 1 min	1,010 L	$3.44	$3.87	$2.13 / $2.84
Fraser Coast council’s assumption (rinse not counted)	400 L/min	3 min + no rinse	1,200 L	$4.09	$4.60	$2.53 / $3.37

How do I backwash my sand filter? Step by step

This sequence is from one media filter maker’s manual; two other makers’ manuals agree on the order and differ only on times.

Note the clean pressure the day the filter is new or freshly backwashed. Every later decision is measured from it.
Turn the pump off. Disconnect any suction cleaner. Never move a multiport valve while the pump runs.
Set the valve to BACKWASH and check the waste hose runs to your permitted drain point.
Pump on, 2–3 minutes, until the water in the sight glass runs clean. Water now flows up through the sand and out of the waste port.
Pump off, valve to RINSE, pump on for about a minute until the sight glass is clear again. Rinse settles the sand bed so dirt does not blow back into the pool. Another maker says 15–30 seconds; a third says about half the backwash time.
Pump off, valve to FILTER, pump on. The gauge should be back near the clean pressure.

Backwash until the sight glass runs clear, rinse until it runs clear again, and never turn the valve with the pump running. If a backwash no longer brings the pressure down, the media maker says the media needs changing; what replacing a pool filter costs prices that.

How much water does backwashing a pool filter use?

Flow × minutes, so it depends on the pump. The media filter maker gives minimum backwash flows of 123–224 L/min by model, 173 L/min for its 25-inch-class models; at 3 minutes plus a 1 minute rinse that is 692 L. One pump maker’s turnover table implies 253 L/min on high, which makes the same 4 minutes 1,010 L. A Fraser Coast council guideline assumes “approximately 400 litres per minute” for 3 minutes: 1,200 L.

The backwash ledger: litres = flow in L/min × (backwash + rinse minutes); one backwash and rinse sends 519–1,200 litres to waste in the five scenarios in the table. To find your own flow, time the waste hose into a 10 litre bucket: litres a minute = 600 ÷ seconds.

Over a year: monthly at 692 L is 8.3 kL, $28.32 at Sydney Water’s $3.41; fortnightly is 18.0 kL, $61.35. Monthly at the council’s 1,200 L is $49.10. That water has to be replaced, which is part of what a pool adds to the water bill; a cartridge filter, cleaned with a hose, produces no backwash at all (how to clean a cartridge filter).

When should I backwash my pool filter?

When the gauge says so, by your own filter’s figure. One media filter maker: 40–50 kPa above the clean reading. One 22-inch sand filter maker: 50 kPa, and at least once a month in a home pool. A glass media maker’s guide: 10 psi, about 69 kPa. A third sand filter maker says 20 kPa in one place and “5 PSI or 35 kPa” in another. The full table of thresholds, and when the media is finished, is on how long a pool filter lasts; this page does not repeat it.

The 22-inch sand filter maker adds a catch: if the filter is connected to mains water, pressure rise is not an accurate indicator because mains pressure fluctuates; rely on the flow. The same glass media guide says sand filters typically need backwashing every 1–2 weeks and glass every 2–3 months.

Where does pool backwash water go?

Wherever your utility says, and the states disagree: to the sewer through an overflow gully in Sydney and Newcastle (NSW rules), not to the sewer for domestic pools in WA (WA rules), the sewer or the garden but never stormwater in South Australia (SA rules), and never the street gutter in Queensland, where backwash is a named contaminant (the street-drain rules and fines). Hunter Water says not during rain; where a pool overflow should go explains why rain is different.

Backwash, rinse or waste: which valve setting?

BACKWASH reverses the flow through the sand to clean it; RINSE runs it forward to waste to settle the bed; WASTE bypasses the filter entirely, which is the setting for lowering or emptying the pool (how to drain a pool). One sand filter maker’s troubleshooting table says sand coming out of the waste line means the pump flow is too high for the filter. If the filter and pump are mismatched, how the pump and filter work together explains sizing, and you can compare pool quotes for a replacement with the rated flow written in.

Common questions

How long should I backwash my pool filter?

Until the sight glass runs clear, usually 2–3 minutes, then rinse for about a minute, says one media filter maker’s manual. Another maker says the rinse takes 15–30 seconds.

How often should I backwash my sand filter?

When the gauge rises by your manual’s figure, 40–50 kPa above clean in one, 50 kPa in another. One sand filter maker says at least once a month for a home pool.

How much water does a backwash use?

519–1,200 litres in our five worked scenarios: 692 L at 173 L/min for 3 minutes plus a 1 minute rinse, 1,200 L at a council guideline’s 400 L/min for 3 minutes.

What does a backwash cost in water?

692 litres costs $2.36 at Sydney Water’s 2026–27 price of $3.41 a kilolitre, $2.65 at Yarra Valley Water’s step 1 rate and $1.46 at Perth’s first tier.

Should I rinse after backwashing?

Yes. Rinse settles the sand bed and flushes loose dirt to waste so it does not return to the pool; makers give 15 seconds to about a minute.

Sources

General information only, current at 2026-10-22. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.

How to backwash a pool sand filter