When you buy bottled water you're buying water by volume at a price set by the company that manufactured it, pre-packaged. They set the price based on the costs

When you buy bottled water you're buying water by volume at a price set by the company that manufactured it, pre-packaged. They set the price based on the costs they incur to bottle it - beyond what you would pay to get the same water as a civilian, in part because creating shelf-stable bottled water is more difficult and expensive than producing regular tap water. To get water, that factory is paying for delivery and treatment infrastructure and ongoing maintenance costs for their equipment. Your water bill similarly covers those ongoing costs. If you buy a pack of bottled water and it leaks, nobody from the bottling company is going to come patch that hole and refill the bottle. This is almost the same as the distinction between paying your electricity bill and buying a pre-charged battery.