This first semester spent working on the Solar Decathlon project aims at defining a compelling concept for the competition. The need for a support for energy considerations was quickly identified to complement the analysis carried out by the architects. This report focuses on how we defined a model dealing with a water and energy supply optimisation for a building. Given the house design the architects came up with, our model allows to determine an optimal energy system, its cost and its environmental footprint by computing how much carbon dioxyde is released. Therefore, various systems able to meet space heating, hot water and electricity demands have been implemented in our model, which is based on the software OSMOSE. A study on rainwater management for grey water supply rounds out the model. We finally tested our model performance with the optimisation and sizing of an energy and water man- agement system supplying two houses.