In our corner of the world, which is an arid region, we typically have water tanks below ground, or on ground, and another tank (or set of tanks) ontop of the house building.

So these days I have been busy replacing the ground water tanks with larger capacity (instead of 1500 Liters, we installed 3 tanks that can hold 5500 Liters total). Top 2 tanks (1000 Liters each) were left as is (fearing that additional water weight may harm the house structure).

We have two types of water. One is the "normal" water from the municipality, used for everything, and two: drinking water. So, we installed a multi-purpose water tank (1500 Liters) ontop of an external room. This tank can be (normally) filled straight from municipal water to serve several purposes from garden irrigation to secondary supply for the laundry room and external kitchen sink. In an emergency, however, it can be separated from municipal water pipe, and filled by tanker and serve as an emergency reservoir for drinking water