A couple of surgeons are at the automobile shop for their Mercedes checkups. They get to sit in a waiting room with their magazines but there is a window into the shop where they can watch the cleanly dressed mechanics assess fluid levels and lubes and diagnostics. Eventually one of the surgeons remarks: "They are doing such precise work with these well built machines. I feel like they are almost doctors like us."
"Maybe," says the other, "let's see them do all that work with the engine running!"

Humans are one of the comparatively few animals to regulate internal temperature through sweat. We usually need more water than we think we do. Different people need different amounts. It changes with gender, age, activity, and one's specific condition and activities. It's usually a good idea to carry some source of potable water with one. In my case I have found that with increased water consumption comes decreased kidney stones. Worth it!