What's The Most Expensive Liquid?

I remember a commercial awhile back about printer ink being one of the most expensive liquids. Ever since then I've thought about this in a whole new light. I used to just buy the cheapest printer. Now, I look first at how much the cartridges will be. I'm even curious about a laser printer that comes with "high yield" cartridges. It seems like if you do a lot of printing you have to pay more for a printer but less per page.