Detention time calculator

A Class C exam topic, not Class D: an extra. Type the tank's gallons and the flow in gpm; you get the minutes, step by step.

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Answer: 190 minutes

Detention time = volume ÷ flow. Gallons ÷ gallons per minute gives minutes.
95,000 gal ÷ 500 gpm = 190 minutes.

Exam-practice math only. It is not an instruction for a real plant, well or tank: for that, follow your system's procedures and ask your supervisor.

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The formula

Detention time in minutes = volume in gallons ÷ flow in gallons per minute.[1]

Which exam it is for

TCEQ's study criteria name detention time in the math of the three Class C water exams (distribution, groundwater and surface water). The Class D math criteria do not name it.[2]

Sources

US EPA Region 6, NPDES Reporting Requirements Handbook, XIII.A Math Formulas, 5. Detention Time: Volume (gals.) ÷ Flow (gpm) = Detention Time (in minutes) (page 30) (read November 13, 2026)
TCEQ, Public Water System Operators: What Applicants for Licensing Need to Know, Need-to-Know Criteria for Class C Water Distribution, Groundwater and Surface Water Operators, Math: detention time; Class D, Math (read November 13, 2026)

Reviewed November 13, 2026. Published by OperadorListo. The sources above are the authority. This is a summary in our own words: check the source before you act on it.