A 20' x 15' filter, water level dropped 12 inches in 3 minutes; what is the rate of filtration in gallons per minute per square foot?

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Multiple Choice

A 20' x 15' filter, water level dropped 12 inches in 3 minutes; what is the rate of filtration in gallons per minute per square foot?

Filtration rate per square foot tells you how many gallons pass through each square foot of filter area each minute. Start with the area: 20 ft by 15 ft equals 300 ft². A 12-inch drop is 1 foot, so the volume drained is 300 ft² × 1 ft = 300 ft³. Convert to gallons: 1 ft³ is about 7.48 gallons, so 300 × 7.48 ≈ 2244 gallons drained. This happened in 3 minutes, giving a total flow of about 2244 ÷ 3 ≈ 748 gallons per minute. Now divide by the filter area to get per-square-foot rate: 748 ÷ 300 ≈ 2.49 gallons per minute per square foot, which rounds to 2.5. Therefore the filtration rate is about 2.5 GPM per square foot.

Filtration rate per square foot tells you how many gallons pass through each square foot of filter area each minute. Start with the area: 20 ft by 15 ft equals 300 ft². A 12-inch drop is 1 foot, so the volume drained is 300 ft² × 1 ft = 300 ft³. Convert to gallons: 1 ft³ is about 7.48 gallons, so 300 × 7.48 ≈ 2244 gallons drained. This happened in 3 minutes, giving a total flow of about 2244 ÷ 3 ≈ 748 gallons per minute. Now divide by the filter area to get per-square-foot rate: 748 ÷ 300 ≈ 2.49 gallons per minute per square foot, which rounds to 2.5. Therefore the filtration rate is about 2.5 GPM per square foot.

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