Final answer:
The T/P relief valve must be located within six inches of the top of a water heater to safely release water and lower pressure if necessary.
Step-by-step explanation:
The T/P relief valve, which stands for temperature and pressure relief valve, is an essential safety feature on a water heater. According to building codes and safety standards, the T/P relief valve should be located within six inches of the top of the water heater. This valve's purpose is to release water and lower the pressure if either the temperature or pressure becomes too high within the tank, preventing potential damage or explosion.