PCL with Web Services, getting error: Are you missing `System.Web' assembly reference?

I am getting this error Are you missing `System.Web' assembly reference? I added the Schools web service as a test and assumed it would have brought in the libs I needed but I guess not.
Now I need to add System.Web I assume but when I go to Edit References > All on the new PCL project its not there, in fact nothing is there :(