A radiation source module comprising a support member, a radiation source assembly connected to the support member, the radiation source assembly comprising at least one elongate radiation source having a source longitudinal axis and a module-to-surface seal disposed on a first elongate surface of the module, the first elongate surface comprising a first longitudinal axis transverse to the source longitudinal axis, the seal operable to provide a substantially fluid tight seal between the first surface and a second surface which is adjacent to the first surface. A fluid treatment system employ the radiation source module is also described.