I'm working on a space opera where the bad guys have amphibious warriors and pilots. This is an engineering and biological question. Assume that the civilization has space fighters of the X-wing and Tie variety, would there be any advantages to filling the cockpit with fresh water? I can think of one problem of economy; it would take a lot more energy to boost a few, cubic meters of water than of air. But assume that is a problem my amphibians have solved--or at least can live with. Are there any other advantages or disadvantages I should be thinking about?