We show how a simple design adaptation creates desirable flow structures that dramatically enhance performance in hollow fiber membrane (HFM) water desalination modules using computational fluid dynamics (CFD) simulations. Conventional HFM desalination modules encase thousands of co-axially aligned HFMs in a mutually parallel flow of brackish water. HFMs are subject to a phenomenon called concentration polarization (CP), which leads to fouling and will eventually prevent clean water production. We found that the twisted HFM module mitigates CP effects and increases transmembrane permeate flux by 5-9% for three flow rates considered. Twisted HFM bundles induce swirling flow structures inside desalination modules that increase momentum mixing throughout. Frictional energy losses and increased pumping power associated with this subtle design alteration are small relative to projected gains in clean water production. We predict system performance increases about 70% for the twisted modules herein considered, and there are in principle no additional required components associated with this geometry adaptation. With our findings, we identify how the twisted module design induces desirable flow structures that increase membrane separation performance by mitigating CP effects and increasing HFM efficacy.