Oh my. Unless you were trying to hit someone with it, chances are that your (one would hope) laptop was powered on at the time. This is unfortunate, as electronics don’t like water, but powered-on electronics, with electrical current running through them, are plain dangerous when submerged into water.
First of all drain the bath tub and fish out your laptop in a safe way – assume that it will give you an electrical shock if you touch water or your laptop with bare hands.
In the unlikely case the laptop has not turned itself off already, TURN IT OFF NOW! Disconnect any cables, external drives etc you may have connected and remove the hard drive as quickly as possible to potentially save your data.
Now you need to leave it out to dry naturally – DO NOT use a blow dryer or anything of the sort. This will take time.
If you would like help recovering your data into a (probably) new computer, let me know.