Work out water tank refill time instantly with clear inputs, formula shown and shareable results.
Fill time is the volume to add divided by the net inflow — supply rate minus any draw-off during filling. Ignoring simultaneous use is the classic error: a 14 L/min supply with 3 L/min being used fills at only 11 L/min, taking a quarter longer.
Refill time
volume to add = capacity x (1 - level); time = volume / (inflow - outflow)
The tank never fills. The calculation returns zero net flow, and in practice the level continues to fall until demand drops.
Time how long a 10 litre bucket takes at the inlet tap and scale up. Mains flow varies with time of day and pressure.