The main difference between PVC and uPVC is that uPVC doesn’t contain phthalates or BPA. This makes it safer for transporting water, as well as making it fire-resistant.
The term PVC stands for polyvinyl chloride, and the term uPVC stands for unplasticized polyvinyl chloride. PVC pipe is often used to distribute water that people aren’t going to drink. It’s also used to insulate electric cables. The uPVC versions often replace wood when building window frames and sills. The uPVC pipe variant also often replaces pipes made of cast iron for drains, waste piping, downspouts and gutters.
Many people use PVC instead of metal, as PVC is much easier to cut than metal, and it’s also easy to use glue together. In addition, PVC is still fairly tough, so not much strength is lost. Most plastic piping around the globe is actually uPVC because of how resistant it is to degradation caused by chemicals, high and low temperatures and various pressure points. The uPVC version of piping is less flexible than regular PVC, but it's also more recyclable.
Neither uPVC nor PVC pipes are used for drinking water. The cPVC variant is used for this purpose instead because it is much safer.