What can i use as a drawing mat?

So i got a new desk. its a great desk but...its cheap so it gets water damage, i didn't really think about this when i bought it but now its kinda of a problem. As you may already now by reading the question/tittle i draw on it and also water color on it ...and im kind off messy when im working on my stuff ( i cant help it). So im wondering what i can use as a drawing mat to put on top of my desk as to not keep damaging it. Any ideas? i would greatly appreciate it cus well; im on a budget and really cant afford to just get a new desk.