The present invention provides: a distributor plate for a composite pressure vessel. The distributor plate includes a thermoplastic polymeric disk having a top side, a bottom side, a perimeter edge and a central opening. Radial slits are formed in the disk to define fluid flow passages through the disk between the central opening and the perimeter edge. The fluid flow passages through the disk are adapted to swirl fluid flowing through the disk from the bottom side to the top side around the central opening. The present invention also provides a water treatment vessel that includes one or more distributor plates, a method for manufacturing a composite pressure vessel that includes one or more of the distributor plates and a method for preparing a composite pressure vessel that includes one or more of the distributor plate for use as a water treatment apparatus.