The pipes are of PVC, CPVC and UPVC. Then how UPVC is differ from previous two

They are all very different. PVC-Polyvinyl Chloride is the base pipe used for cold water and drainage piping. CPVC is Chlorinated PVC, modified PVC used for hot and cold water piping. UPVC is un-plasticized PVC, hard, rigid piping used only for drainage, primarily used to replace cast iron piping. Not approved for water distribution, I have never encounter in Atlanta area. Unless you have an old house in Atlanta, all drainage is Schedule 40 PVC.