Estimate gallons lost based on flow rate and time.
This calculator estimates how much water leaves the pool during backwashing. Enter the approximate backwash flow rate in gallons per minute and the number of minutes the filter is backwashed. The tool multiplies those values and shows the result in gallons and liters.
The estimate is useful for planning refill water, understanding seasonal water use, and tracking how backwashing affects salt, stabilizer, and other dissolved chemicals.
Every backwash removes treated pool water. That lowers the water level and carries away chlorine, salt, cyanuric acid, calcium, and other dissolved material. Frequent or overly long backwashing can increase water cost and chemical replacement cost.
Actual flow depends on pump size, pump speed, plumbing diameter, filter type, valve position, discharge restrictions, and filter condition. A variable-speed pump may produce very different water loss at different RPM settings.
Follow the filter manufacturer’s directions. Many systems are backwashed until the sight glass or discharge water runs clear, then rinsed as required.
A flow meter is best. You may also use pump data, plumbing estimates, or a safe discharge-volume test where permitted.
Yes. Any dissolved material leaves in roughly the same proportion as the water removed.
Yes. Rapid pressure rise may point to heavy debris, algae, undersized filtration, channeling, or a filter that needs inspection.
Do not backwash by the calendar. Use the filter’s clean starting pressure and backwash when the pressure rises according to the manufacturer’s guidance.