Hydration is a survival mechanic introduced in Experimental Rust.
If you look down directly at streams and rivers you can drink from them directly as well.
Your thirst level is indicated by a blue bar above the Hunger bar. If this bar drops below 50, you will begin to lose health until you die or find a source of water. If the player becomes fully dehydrated, their movement speed will be significantly reduced.
The level cannot be reduced below zero; therefore Cooked Human Meat can be consumed in quantity without ill effects if hydration is restored from zero afterwards. This will not work with Salt Water, however, as it has no beneficial effects, and gives the Poisoning status also.