Biofiltration is a simple and low-cost method for the clean-up of contaminated waters. Reduced chemical availability to surface-attached degrading bacteria however may limit their efficient use. When a direct current (DC) electric field is applied to an immersed packed bed, it invokes electrokinetic processes such as the electroosmotic water flow (EOF). EOF is a surface charge-induced, plug flow-shaped movement of pore fluids. It acts at a nanometer distance above surfaces and provokes the mobilization of fluids that are typically unaffected by hydraulic flow. EOF therefore has the potential to change microscale pressure-driven flow profiles and to promote the availability of contaminants to microbial degraders. In laboratory percolation columns we here assessed the effects of a weak DC electric field (on the biodegradation of waterborne naphthalene (NAH) by glass bead attached Pseudomonas fluorescens LP6a. To vary NAH bioavailability, we used different NAH concentrations at C0 > Km and hydraulic flow velocities at ranges typical for biofiltration systems ( = 0.2 – 1.2×10-4 m·s-1). In DC free controls we observed higher specific degradation rates (qc) at higher NAH concentrations. At given C0 however, qc decreased with increasing suggesting bioavailability restrictions depending on the hydraulic residence times. Relative to controls, DC fields increased qc and resulted in linearly increasing benefits up to 50% with raising hydraulic loadings. We interpret these benefits by EOF promoted NAH bioavailability to cells. As the EOF acted opposite to hydraulic flow, it modified pressure-driven flow profiles around the collector beads at microscale and, thereby allowed for better NAH provision to the cells exposed to zones of low NAH bioavailabilty. To our knowledge this is the first description of the superimposition of EOF and pressure-driven flow on the bioavailability of waterborne chemicals. Electrokinetic approaches may give rise to future technical applications that allow regulating biodegradation of waterborne contaminants.