Formula and example
How it is calculated
Net flow=inflow₁+inflow₂−outflow. Time=capacity·(target fraction−initial fraction)/net flow.
Worked example
A 1,000-litre tank needs to rise from 20% to 80%. At a net inflow of 10+5−3=12 l/min, the time is 600/12=50 minutes.
Things to check
- Inflows and outflow are assumed constant. In practice, flow through a bottom drain may vary with the water level.
- If the net flow is zero or moves away from the target, a different target level cannot be reached.
Frequently asked questions
Can I also calculate draining time?
Yes. Choose a lower target and an outflow greater than the inflow. Both volume change and net flow are negative, so duration remains positive.