Good question. This is one many business owners do not consider, so bravo for thinking about it. And the answer is yes, you could be sued. Your best course of action would be to have an Indemnification Agreement between you and the plumber, that says that if you are sued, he agrees to "make you whole" (i.e., reimburse you.). It would not stop you from being sued (because anyone can sue anyone, really), but it would cause reimbursement from the plumber in the event that you were sued for something he did. (Of course, if it is your actions that caused the suit, the Indemnification Agreement would not kick in.)
So, yes, you can be sued, and yes, you can take some steps to put yourself in a better situation. Let me know if you'd like to discuss further.
Best of luck. Congratulations on your website!
Attorney Diana L. Bartolotta