The 'u' in uPVC stands for 'unplasticised.' That means it does not contain any phthalates, which in turn means it is fire-resistant and can transport water more safely. PVC is typically used to transport water that isn't meant for human consumption, as well as in electrical cabling.
uPVC is usually used in place of wood when constructing windows, as well as in place of cast iron when making drains, downspouts, and gutters.