Operator terms · Water and wastewater
What is detention time?
Detention time is how long water stays inside a tank or basin, found by dividing the tank volume by the flow rate. It is why a clarifier can settle solids or a contact basin can disinfect: the water needs enough time in the tank. Too little detention time and the process does not finish.
Last reviewed 2026-08-03
The simple formula
Detention time equals tank volume divided by flow rate, in matching units. A bigger tank or a slower flow means more time inside.
Why it decides the outcome
Settling and disinfection both need time. If water passes through too fast, solids do not settle and disinfectant does not finish its work.
Common questions
- How is detention time found?
- Divide the tank volume by the flow rate, in matching units.
- Why does it matter?
- Settling and disinfection both need enough time in the tank.
- What lowers detention time?
- A higher flow rate or a smaller tank.