all depends on your requirements, how many in your household? access to your front /rear gardens for siting the tank.
I put mine in the front garden, as i have a small lawn at the front and had planned to block pave my drive. At the time of doing this i opted to dig up my lawn and put the tank...
Have installed my own rainwater harvesting system, as water efficiency is my job.
3000ltr tank in my front garden , my toilets are flushed with rainwater, my washing machine is hooked up to rainwater and also the garden taps back and front.
It's the way forward....