Where is the best location to place my water tank?

This is governed by several factors:

Slope of the site

The most suitable site will be on level ground, away from retaining walls. Extra installation expense may be incurred if your site needs to be excavated to make a level foundation.

Downpipe location

You should aim to connect as many downpipes to feed your tank as is practical. The closer the water tank is to your downpipes, the more efficient the water harvesting system will be. If downpipes need to be diverted and run horizontally over long distances then the installation expense will increase, and the efficiency of the system may be compromised.

Aesthetics

While a well-positioned water tank can add a design element to your home, most people are not likely to install a water tank where it is highly visible. This is an important consideration.

Proximity to laundry or toilets

Where a water tank is used to feed a toilet or washing machine, a licensed plumber must install it. Again, the shorter the run of pipe work from the tank site to the internal appliance, the less expense will be incurred in installation