I do the whole thing with WFP, the only time I won't use it is on windows where the paintwork has oxidised (gone powdery, you can check for this by wetting a finger and wiping it on the frame, if it comes of the colour of the paint, then the frame has oxidized, and with WFP you continually draw down this residue and can leave a milky film on the glass. You can get it fairly good with WFP, but in all fairness, on windows auch as these you will never do as good a job as you will with traditional methods of window cleaning.)
You have to watch out for the odd leaky door or window, but that's about it for me.
Water usage on a standard 3 bed semi?.....Between 15 and 20 litres.
If you clean all t he windows with EFP then an average day should see you get through anything from 200L to 300L So far I've rarely used more than that, but I've known some go through a 1000L in a morning
Time taken for am average 3 bed semi, with standard UPVC windows normally takes me no more than 10 minutes.
Regards,
Ian