The present invention provides a radiation source module for use in a fluid treatment system. In one embodiment, the module comprises: a substantially elongate first support member having a longitudinal first axis; and a first pair of radiation source assemblies extending from the first support member, each radiation source assembly comprising a radiation source; wherein the first pair of radiation source assemblies is oriented such that a second axis extending through a center point of each radiation source assembly is disposed at an angle with respect to the first axis. In another embodiment, the module comprises a substantially elongate first support member having a longitudinal first axis; and a first column of radiation source assemblies extending from the first support member, and a second column of radiation source assemblies extending from the first support member, each radiation source assembly comprising a radiation source; the first column of radiation source assemblies and the second column of radiation source assemblies disposed adjacent one another.