Natural Selection Seems Insufficient

[OakTree500]

But when I get thirsty, I  need to go find water NOW. I can't wait thousands of years.

The evolution part is having thirst for water like, at all.

You've had the signal that says "you need to drink some water" - and if you don't drink, that is your choice [being a human being who can actively ignore such a thing until you are about to die really]

Thirst as a point would have been something that evolved over time as well - as in, there would have been organisms that needed water and a chemical signal to the brain to say "you should drink something now" didn't evolve and they died. The fact you have thirst in the first place shows that evolution has occurred because you have the ability to be thirsty. 

Some organisms will have naturally hydrated, for one reason or another, while other organisms will have died off entirely because they didn't - many shared "chemical signals" prove we have a common ancestor to some degree also.