A portable micro-organism inactivation system comprising: a casing mounting, a UV radiation source, a pump, and releasable tube support for supporting an elongate tube to define a flow path extending therethrough which is substantially free of substantial discontinuities are provided by the present invention. The elongate tube has a first portion and a second portion wherein the first portion has a UV-transparent wall. The first portion extends in close proximity to the UV radiation source within an irradiation zone thereof while the second portion is interfaced with the pump for pumping of fluid through the system so that substantially the whole of said individual fluid unit is exposed to a similar micro-organism inactivating level of UV-irradiation, while minimizing damage to the desired components thereof. The invention also provides a method of micro-organism inactivation in a fluid using a system of the invention.