If it is under the slab, then it is not likely to be plastic. ALl the plastic systems I have ever seen were overhead. You probably have a leak in a copper hot water pipe under the floor.: I have recently developed a leak in my home which is not quite 10 years old. To make it worse the leak is under my slab. I have been told plastic pipeing was used by the builder. I have heard that there have been problems with certain plastic pipes. How can I determine the type of piping used in my home ie. pvc vs polybutelene. : Any help with regards to this matter will be greatly appreciated.