An apparatus for the treatment of water includes an elongated housing having a first end and a second end. The first end has a water inlet and the second end has a water outlet. An elongated ultraviolet radiation source with a sleeve is concentrically located within the elongated housing. The elongated ultraviolet radiation source has, at its first end, electrical connections, which extend through the second end of the housing and have a second free end held in a support element. The support element includes a supporting structure containing a ring element and from thereon radially inwardly running arms. The arms are designed in such a way that during assembly the arms are resiliently deformed and wherein, if assembled, the arms are pressed against the sleeve, so that the free end of the ultraviolet radiation source is held by the arms in a resilient manner.