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Calcimator

Backwash Water Calculator

Calculate filter backwash volume, frequency, and supply requirements for water treatment plant filter maintenance.

Inputs

sq ft
gpm/ft²
minutes
hours
gpm/ft²

Results

Volume per Backwash (per filter)

60K gallons

Daily Backwash Volume

124.8K gallons

Backwash % of Production1.4%
Peak Backwash Flow6,000 gpm
Supply Tank Size74.9K gallons
Backwash Pump Size61 HP
Rise Rate24.1 in/min
Est. Bed Expansion48%
Backwashes per Day0.5
Annual Backwash Volume45.6 MG
Annual Backwash Cost$137,210.00
Peak BW Flow MGD8.64
How to Use This Calculator
  1. Enter Filter Area (sq ft per filter) and Number of Filters in the plant.
  2. Set Backwash Rate (gpm/ft²) based on your filter media type — typically 12-20 gpm/ft² for sand filters.
  3. Input Backwash Duration (minutes) and Filter Run Length (hours) from your operational records.
  4. Add Surface Wash Rate (gpm/ft²) if your filters use a surface wash system in addition to backwash.
  5. Review Volume per Backwash and Daily Backwash Volume (K gallons) to size your backwash supply tank.
  6. Check Backwash % of Production to ensure recovery losses stay within permit and efficiency limits.

How the result changes with Filter Area (per filter)

Filter Area (per filter)Volume per Backwash (per filter)Daily Backwash Volume
20931.4K gallons65.2K gallons
707106.1K gallons220.6K gallons
1,304195.6K gallons406.8K gallons
1,801270.2K gallons561.9K gallons

What each input means

Filter Area (per filter)
Surface area of each individual filter bed.
Number of Filters
Total number of filter cells in the plant.
Backwash Rate
Backwash flow rate per unit filter area. Typical: 12-20 gpm/ft².
Backwash Duration
Duration of each backwash cycle. Typical: 8-15 minutes.
Filter Run Length
Average time between backwashes. Typical: 24-72 hours.
Surface Wash Rate
Auxiliary surface wash rate. 0 if no surface wash system. Typical: 1-3 gpm/ft².

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Filter Area (per filter) = 400, Number of Filters = 4, Backwash Rate = 15, Backwash Duration = 10 = 6 input(s) provided
  2. Calculate Volume per Backwash
    Volume per Backwash
    60 = 60
  3. Calculate Daily Backwash Volume
    Daily Backwash Volume
    124.8 = 124.8
  4. Calculate Backwash % of Production
    Backwash % of Production
    1.4 = 1.4
  5. Calculate Peak Backwash Flow
    Peak Backwash Flow
    6000 = 6000

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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