A fluid flow modifier device comprising: an inlet portion for receiving a flow of fluid; an outlet portion for outputting the flow of fluid; and a flow modifier portion disposed between the inlet portion and the outlet portion, the flow modifier portion comprising an outer portion comprising a closed cross-section to the flow of fluid and an inner porous portion configured such that at least a portion of the flow received in the inlet portion must pass through the inner porous portion to reach the fluid outlet. The fluid flow modifier device is ideally used to transition fluid flow between an fluid supply line and a fluid treatment zone—for example, a pressure water supply line and an ultraviolet radiation treatment device (e.g., drinking water treatment device).