What is the minimum size of water supply required for a water closet flush valve type?

The minimum size of water supply required for a water closet flush valve type is indeed 1 inch. A flush valve is designed to quickly release a significant volume of water to effectively clear and refill the toilet bowl. This requires a larger diameter pipe to ensure that there is adequate water flow and pressure during the flushing process.

Using a 1 inch supply line helps to prevent issues such as insufficient flushing power or delays in bowl refill time, which can lead to user dissatisfaction. In contrast, smaller sizes such as ½ inch or ¾ inch do not provide the necessary flow rates for flush valve toilets. The 1 ½ inch option, while larger than necessary, is typically used for drainage rather than supply lines, making it inappropriate for this application. Thus, 1 inch is established as the standard minimum for optimal performance of a flush valve water closet.