The Home Inspectors I work with tell my Clients if they find something they believe the Home Inspector missed, please contact them and they will be willing to discuss options.
I have had a Home Inspector do a repair on something they missed.
I have no idea what the Home Inspector you used has for a policy, but you may want to contact them, and see what they have to say.
You may also want to get a contractor's opinion of what the cause is and cost to repair, so you know what is what when you speak to the Home Inspector.
Best of luck!
It seems that you need to contact the inspector - and your lawyer.
But I think another good suggestion is to call a plumber and fix the leak while you pursue the others.
(Please note: when you choose an answer as a Best Answer, or at least give a thumbs up, it helps those who answer questions here.)
So: Should the inspector have been able to detect the leak? If so, then you should have some recourse against him. Otherwise, no.
And, as others note, it's up to you to get the leak fixed. Incidentally, if it's a frozen pipes problem, then it's likely you've got other problems, too.
Hope that helps.