This is a question that has plagued me for years. It's known that diarrhea/watery stool is a side effect of being dehydrated, which is extremely counterintuitive to me. I understand that your body functions poorly when dehydrated and that causes your large intestines to not filter water out as efficiently, but doesn't that make the human body seem kind of dumb, or at least fatalistic as it basiclly increases the pace of your demise if you're legitimately trapped and dehydrated? We have evolved over millions of years (or 6,000 depending on what you believe), so why wouldn't our bodies have adapted to conserving water when we are in a position of lacking hydration? If anything, stools should be harder when you are dehydrated as every last drop of water is squeezed out by your large intestine. I know this line of thought is gross, but I have honestly wondered this off and on for at least five years.