What is the required type of valve for every water closet?

The required type of valve for every water closet is a shutoff valve. This valve is essential because it allows for the control of water flow to the toilet independently from the rest of the plumbing system. Having a shutoff valve installed makes it possible to easily isolate the water supply when maintenance or repairs are needed, helping to prevent leaks or flooding.

In residential plumbing, a shutoff valve is typically located near the base of the toilet, enabling quick access in case of emergencies. It allows the user to turn off the water supply without affecting other fixtures in the home, which is particularly important when dealing with repairs or cleaning tasks.

The other options serve different functions. A ball valve is a type of shutoff valve but is not specifically required for a water closet; a check valve prevents backflow but is not necessary for toilets; a pressure relief valve is used to release excess pressure in systems to prevent damage, which isn't a function that pertains directly to the operation of a water closet.