Filter, waterway control system and water heater

The invention discloses a filter, a waterway control system and a water heater, the filter comprises: a housing, wherein a cavity is formed in the housing, and the housing is provided with a raw water pipe and a purified water pipe which are communicated with the cavity; a filtering assembly which is arranged in the cavity, wherein the filtering assembly is used for filtering raw water input from the raw water pipe to generate purified water, and the purified water is output from the purified water pipe; a sensor assembly which comprises a flow measuring element arranged in the raw water pipe and/or the purified water pipe, and/or a temperature measuring element arranged in the raw water pipe and/or the purified water pipe. The water flow detection of the raw water pipe and/or the purified water pipe of the filter is realized by adopting the sensor assembly arranged on the raw water pipe and/or the purified water pipe, and the sensor assembly is arranged in the raw water pipe and/or the purified water pipe, s