Hazel if you think in terms of 1 & 1/2 -2 litres a day then use a half litre bottle it doesn't seem so much. A half litre bottle isn't very big and I keep it nearby refilling it when it's empty. It's surprising how quickly you find yourself refilling for the third time. It's worth doing because if you're well hydrated it's much easier to resist temptation believe it or not.