Supply fittings are designed for a rated supply pressure of 690 kPa (100 psi) and functional between 140 and 860 kPa (20 and 125 psi). See ASME A112.18.1 / CSA B125.1.
The majority of plumbing fixtures are designed to operate at 55psig. Flush valves, ballcocks, faucets are all designed to operate normally at this pressure.