David,
Yes, it would. After your initial cleans, your should be able to clean (tops only), four or five semi-detached houses per 18 litre fill.
I think it's around 4 litres to a gallon, so in theory your RO/DI unit should produce 200 litres per day; however I think this is only if you have the correct water pressure; a fairly high one.
So you'll probably produce less than 200 litres per day.
But I/We clean many more houses than eight per day; tops only; using around 100 to 150 litres per day.
However, in the winter, unless you've a garage (which I haven't, or a frost-protector of some description; which I haven't); it's not a good idea to leave your RO/DI unit out all night because RO membranes don't like the frost apparantly.
I've a 200 Gallon per day RO/DI which does me, since it can make enough pure water during the day (which is normally above zero-degrees-celcius) to satisfy my needs and during the winter-nights I can stick it under the stairs to stop it from freezing and damaging the membranes.