A non-return valve (19) for a water supply system (1) or a pump (4) is integrated in a flow channel (14) of the water supply system (1). The non-return valve (19) includes a sealing body (21) which is mounted within the channel (14), blocks the channel (14) in a first position forming the closure position and releases the channel (14) in a second position forming the opened position. The sealing body (21) is movably arranged on a holder (31) which includes a closure body (15), with which the holder (31) is releasably fastened in a housing opening.