Water purifier, flow billing system and method for water purifier

The invention discloses a water purifier and a flow billing system and method for the water purifier. The flow billing method for the water purifier comprises: a flow meter is arranged behind an RO (Reverse Osmosis) membrane, meters water flow flows through the pure water side of the RO membrane, subjects the flow to being generated into digital signals, and transmits the digital signals to a processor of the water purifier; the processor calculates and stores corresponding fees according to single-time flow information, and simultaneously sends calculated results to a remote server through a wireless communication module; or the processor utilizes the wireless communication module to directly send flow data metered by the flow meter to the server, and the server calculates the corresponding fees according to the flow data; and the server inputs account data of corresponding users according to fee information which is sent by every water purifier or calculated by the server. The flow accounting method for the