Question: how many litres in a big bottle of water?
Answer: For the more common 500 mL bottle (aka 16.9 fl oz in the US), the answer is 2. I have also seen 1 L bottles, and a lot of soda comes in 2 L bottles. There is no “standard” bottle size, but a bunch of quasi=standard sizes. Four big water bottles can hold 8 gallons of water.