At least get a back pac for those 3 storeys,
The tds will be high where you are so you cant just use resin, get a cheap ro and upgrade as you go or take the plunge and get a 4040 ro which will produce faster water ive got a 4040 and put it on at 9 and turned it off at 4.30 after producing 1000 litres of water, have you got a garage or shed you can put a tank.