Where does the coolant go?

[detroiter]

I don't have any leaks in the system or anything that I'm aware of but just wondering where it is exactly that coolant goes and why it needs to be topped off every so often if their is no leaks? Does it just somehow evaporate?

[Yaris Hilton]

Water in the overflow tank does evaporate, but it's a very slow loss. If you're having to top up often, you've got a little leak somewhere.