[en] DEEP is a Desalination Economic Evaluation Program developed by the International Atomic Energy Agency (IAEA) and made freely available for download, under a license agreement (www.iaea.org/nucleardesalination). The program is based on linked Microsoft Excel spreadsheets and can be useful for evaluating desalination strategies by calculating estimates of technical performance and costs for various alternative energy and desalination technology configurations. Desalination technology options modelled, include multi-stage flashing (MSF), multi-effect distillation (MED), reverse osmosis (RO) and hybrid options (RO-MSF, RO-MED) while energy source options include nuclear, fossil, renewables and grid electricity (stand-alone RO). Version 3 of DEEP (DEEP 3.0) features important changes from previous versions, including upgrades in thermal and membrane performance and costing models, the coupling configuration matrix and the user interface. Changes in the thermal performance model include a revision of the gain output ratio (GOR) calculation and its generalization to include thermal vapour compression effects. Since energy costs continue to represent an important fraction of seawater desalination costs, the lost shaft work model has been generalized to properly account for both backpressure and extraction systems. For RO systems, changes include improved modelling of system recovery, feed pressure and permeate salinity, taking into account temperature, feed salinity and fouling correction factors. The upgrade to the coupling technology configuration matrix includes a re-categorization of the energy sources to follow turbine design (steam vs. gas) and cogeneration features (dual-purpose vs. heat-only). In addition, cost data has also been updated to reflect current practice and the user interface has been refurbished and made user-friendlier