UV light emitting diodes (UV-LEDs) with peak emissions at 265,280 and 310 nm were applied to batch and flow-through water disinfection systems. Inactivation efficiency of Escherichia coil was compared between reactors and among emissions based on the exposure time and fluence. Combined emissions at 265/280, 265/310,280/310 and 265/280/310 nm were also tested in the flow-through reactor. The time-based inactivation efficiency was highest with the 280 nm UV-LED while the fluence-based efficiency was highest with the 265 nm UV-LED. In the batch reactor, the UV-LEDs at 265 and 280 nm achieved over 4 log inactivation of E. coil at fluences of 10.8 and 13.8 mJ/cm(2), respectively, while the UV-LED at 310 nm required 56.9 mJ/cm(2) for 0.6 log inactivation. The flow-through reactor showed tailing in the fluence-response curves and resulted in lower inactivation efficiency than the batch reactor, with lower fluence-based inactivation rate constant of 29% for 265 nm and 32% for 280 nm. Combined emissions were less efficient than the component emissions applied separately, and reduced output power for each UV-LED was observed for combined cases. This study provides key implications for the future application of UV-LEDs to water disinfection systems. (C) 2013 Elsevier B.V. All rights reserved.