Well, it is possible to use plastics as it is described in the WHO GOOD MANUFACTURING PRACTICES (GMP): WATER FOR PHARMACEUTICAL USE (WPU) - Working document QAS/04.047/Rev.1.
“Appropriate plastics and stainless steel materials are acceptable for WPU systems.”
“Suitable materials that may be considered for sanitary elements of the system include 316 L (low carbon) stainless steel, polypropylene (PP), polyvinylidenedifluoride (PVDF) and perfluoroalkoxy (PFA). Other materials such as unplasticized polyvinylchloride (uPVC) may be used for non-hygienic designed water treatment equipment such as ion exchangers and softeners.”
But I don’t think it is a good idea to use PVC, because (exempt if I’m wrong and if the technology is better than before) to link PVC components, you have to use glue which with the time will desintegrate in the purified water, which is not recommended. In my experience, maintenance services are not really agree with this material because, with the time, they had a lot of repairs to do on water distribution (mainly near the pumps), because of the lose of glue in the joint, … Moreover, the leaks caused floods in technical zone and so a lot of troubles…
So I don’t recommend that material for my part…
I hope I help you.