Exam math · Flow
Detention time
How long water spends in a basin: the volume divided by the flow through it.
The formula
Detention time = volume divided by flow, with matching units.
The unit trap
Volume in gallons over flow in gallons per minute gives minutes; over gallons per day gives days. Most misses here are unit mismatches, not arithmetic.
Worked practice example
A practice basin holding 60,000 gallons with 2,000 gallons per minute flowing through detains water 30 minutes. (Invented numbers.)
On exam day
A formula and conversion table is provided with the standardized exam; the official version is published by the exam provider at gowpi.org. These pages teach the concepts in our own words so the sheet on the desk reads as a reminder, not a puzzle.
The rest of the math
| Volumes | Tank volume |
| Volumes | Pipe and cylinder volume |
| Flow | Flow and velocity |
| Treatment math | Chemical dosage |
| Treatment math | Percent strength and dilution |
| Treatment math | Removal efficiency |
| Hydraulics | Pressure and head |
| Hydraulics | Pump and horsepower math |
| Foundations | The conversion backbone |
| Foundations | Averages and loading rates |
| Foundations | The formula-first method |
The operator math sheet
One printable page: the exam format, the formula-first drill method, and the unit-conversion discipline that decides the math questions. Free.
No spam. One useful sheet and occasional notes.