Calm down! Calm down!
If they keep the water on then you have to use plan A - If they turn it off from time to time - plan B. If it's standpipes - plan C!
Plan A - as the hysteria builds among the customers, then in proportion to it show willing and do more trad. than before. Just wfp the tops (not many patio doors up there!) and blade the bottoms - so now on a three bed semi your wfp'ing four or five windows instead of ten windows/doors. If no-one's about to moan then do the downstairs wfp as water permits.
This means that if you're careful you'll use 8 to 10 litres instead of 16 - 20 plus.
Plan B - if they turn the water off at times then stick with plan A but apply it more stringently.
Save your waste water from your R/O for when you need to do trad.
Plan C - Just do trad downstairs and tell 'em you'll do upstairs when the drought's finished. (Charge them three-quarters of the price cuz there's more glass downstairs.
) Go to the standpipe with a couple of 5 gallon drums. One will last all week on trad.
Sorted!
I think the real problem is looking folk in the eye and carrying on while they moan about not watering their lawns and cleaning their cars!