Backwash Water Volume Calculator

Work out backwash water volume instantly with clear inputs, formula shown and shareable results.

About Backwash Water Volume Calculator

Backwash volume is filter area times backwash rate times duration. Rates of 30-40 m/h are needed to fluidise and expand sand media by 20-30%. Backwash water typically consumes 2-4% of plant output, and recovering it after settling is standard practice where water is scarce.

Formulas

Backwash volume

Volume = filter area x backwash rate (m/h) x duration (h)

Flow rate

Flow (L/s) = area x rate x 1000 / 3600

Worked example

With the default values below, Backwash Water Volume Calculator returns Volume Per Backwash of 144.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Filter Areaminimum 0 m2: 30 m2
Backwash Rateminimum 0 m/h: 36 m/h
Backwash Durationminimum 0 minutes: 8 minutes
Backwashes Per Dayminimum 0: 4

Results

Volume Per Backwash: 144.00
Daily Backwash Volume: 576.00
Backwash Flow Rate: 300.00
Annual Backwash Volume: 210.240

Step by step

1Values used
2Backwash volume
3Flow rate
4Volume Per Backwash= 144.00
5Daily Backwash Volume= 576.00
6Backwash Flow Rate= 300.00
7Annual Backwash Volume= 210.240

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Can backwash water be recycled?

Yes, after solids removal, but recycling concentrates pathogens and disinfection by-product precursors. Many regulators cap the recycle rate and require it to be returned upstream of all treatment barriers.

What if the backwash rate is too low?

The bed does not fluidise properly, mud balls form, and the filter progressively loses capacity and allows breakthrough. Air scour combined with a lower water rate is often more effective than water alone.