Pending Level 4 Water Restrictions

[efc]

With my new system being planned I have tried to recycle as much water change/ waste water as possible.
The plan is to have a 2000L + water tank taped to the guttering of our house as well as being supplemented with all water change water (currently being put on the lawn).
The poly tank will have a 4 stage R/O filter plumbed to it and this will fill my 6x2x2 water change holding tank. The tank will slowly be filled with R/O water as it can only filter approx. 100L or so a day.
R/O filters can apparently take out as much as 95% of heavy metals and chemicals in the water so it will be better water then what i'm probably using now.

If all goes well I may not ever have to use mains water again for the tanks.
The only problem that this idea has is the fact rain may never fall again and the poly tank will eventually run dry due to evaporation.