Importance of roof surface

We learnt from our Airbnb owner how important is it to buy a house with a big roof. In Queensland many houses are NOT connected to town water, which means you have to be self-sufficient and collect as much water as you can when it rains. 1 Mm of rain on 1 m² roof surface, gives 1 liter water. As an average you should best have a roof with a surface of 500 m² and several collecting tanks. For a family of 5 people you should have water storage capability of around 100 000L, meaning you need several tanks of 25 000L and/or 15 000L. Different from Belgium, tanks are visible (as here is space enough) and not underground. Another important element is of course the pumps and were you position your tanks. It is always a good idea to position your tanks a bit higher than your house, in case the electricity get cut (by a storm) and pumps can’t work.