Not just water. You're forgetting:
Coke/Soft Drinks
Milk
Juice
Fresh Coffee
V/Red Bull etc
People buy all those things and pay anywhere up to $5 for 250ml!!!!!!!!!!!!!!
None of those things make your car run and with the exception of milk, none of them really need to be bought at all (can make your own juice at home and the others are just luxuries). If you want your car to run. Buy fuel. If you don't want to pay for fuel, don't own a car. But don't cry poor when you can pay $3.80 for 600ml of Coke.
I never even look at the price of fuel. I don't give a rats. I hold the lever until it clicks off, then I go in and tell them what pump number, swipe my card, key my pin, and leave.