> I personaly use 4 500ml (total of 2 litres) mineral-water flasks

That's what I keep in my bug-out bag. My every-day carry doesn't include any water at all. I have about 3 litres in my car.

I keep more water in the house for shelter-in-place. About 40 litres of bottled water, and there is probably about 140 litres in the cold water tank and some more in the hot water taknk. I also have an aquarium with about 150 litres and know of a nearby stream.