PVC pipe is a no-no.
This water heater has a 1/2″ PVC extension tube on its temperature-pressure relief valve. PVC stands for Polyvinyl chloride, but a more suitable name might be “Pipe Very Cracky”. The piping is brittle and not rated for use inside a home generally, and especially not as an extension tube on a water heater temperature-pressure relief valve. In addition to this improper material the extension tube is undersized – it should be 3/4″ pipe. If the valve were to open, the high temperature and pressure of the water could easily splinter the piping. A temperature-pressure relief valve should have a suitable extension tube installed – allowable materials include 3/4″ copper, galvanized steel, CPVC, or PEX piping.