On average one person uses 1 litre of water per minute. So therefore 250 litres = 250 minutes worked = 4 hours. Bearing in mind that once mastered, using a water fed pole is 3 to 4 times faster than traditional window cleaning.
So 4 hours with a pole is like 12 to 16 hours ladder work.
The first time you use a pole you should spend as long as you would using a ladder washing and thoroughly rinsing the glass, then you shouldnt have any problems with spotting.
Glyn
Omnipole