[user104658]

Where is a family of 4 storing 120 litres of water .

Meh. I'm lucky enough to live within walking distance of a drinkable water source (thus effectively unlimited water) and probably have 5 or so days worth of food kicking about at any given time. If the **** hits the fan so badly that you need a significant amount of stockpile food and water, then all that stockpile is going to do is give you a couple of extra days before you're in the same position as everyone else.