I have had an aquatec trolley since early February and first time around my 8 barrels (200 litres) were being used at 1 x 25 litre barrel per semi-detached (with bay windows but not too large) - second time around about 15 litres per semi. But I do run out early afternoon or I spread it out by doing upper floors only to save water. (and blading the bottoms)
I am paranoid about rinsing and having a TDS reading between 000 and 003, and am pleasantly surprised at the positive response from customers. (literally only one out of eighty so far has made a negative comment and no-one has complained after my second visit. Early days yet though!)
Shortly I am increasing my capacity by buying a trailer and I am confident that the 400-450 litres (inc car) I then carry will be enough.