Greetings Vane welcome to the Forum.
I hope what you mean by "water", is a 50/50% mix of Coolant. If you don't protect your cooling system with that stuff, you're doomed !
One of the most common problems when Overheating occurs without leaks, is low pressure in your system. Water boils at 212°. and without any pressure on it, via the Radiator Cap, the water boils and is discharged via the overflow. Today's engines will have temperatures well above what that takes.
So, check or replace the Radiator Cap, make sure the Coolant is of sufficient proportion, and we'll see if that doesn't fix your problem.
Have a good Day !
S.W.