Once you have the first cleans out of the way, then a backpack will be enough water for a house.
Think about getting a larger RO - 100GPD isnt much - they never produce 100GPD (thats US gallons)
Also i'd suggest getting a few 200L water butts .... best to have more water than not enough
Once you get the backpack, you could convert this to a trolley with the bits from the backpak and have 25L barrels instead
Go for a clx - slx ..... Dazmond is spot on in what he says.