Interactive River-Aquifer Simulation-2010 (IRAS-2010) is a generalized water resource system simulation model. IRAS-2010 is a new release of IRAS previously released by Cornell University in 1995. Given hydrological inflows, evaporation rates, water allocation rules, reservoir release rules, consumptive water demands and minimum environmental flows, IRAS-2010 estimates flows, surface water and groundwater storage, water use, energy use, and operating costs throughout the water resource network at each user-defined time-step. Multi-reservoir release rule curves, streamflow routing, regional groundwater flow, ecological flows, hydropower, pumping, desalination, and other features can be represented. The IRAS-2010 model is linked to a generic user-interface called HydroPlatform; both model and user-interface are open-source. We present an IRAS-2010 model of London's conjunctive use water resource system that satisfactorily emulates a more sophisticated model currently used by regulators. Results from daily and weekly time-step models are compared. IRAS-2010's fast run times make it appropriate for workshop settings and advanced planning methods that require many model evaluations. Model limitations, benefits, project organization and future plans are outlined. (C) 2011 Elsevier Ltd. All rights reserved.