As Smurf says it depends on the flow from the customers tap, but you have the same problem with any non fixed tank, a larger 240L wheelie bin will only provide about 15mins of cleaning from full to empty, so if the tap flow is not 15lpm or more you will be waiting for water. What I have found is that with a tall and narrow (although smaller capacity) wheelie bin I can get cleaning again quicker if the flow is slow, than waiting to fill a larger tank (may all be in the mind!).
The only way to really keep working with low tap pressure is to use a van mounted tank and arrive full of water.
Neil