Résumé
This study is a part of a research program based on two observations :Observation 1: drinking water demand in Mediterranean area is characterised by a peak during summer due to seasonal population inflow combined with more significant water requirements during this period to satisfy external uses (gardens, swimming pool, etc). Such a situation leads urban water managers to dimension water infrastructures in order to answer to the upper water demand. This is expensive and has a negative impact on water price.Observation 2: a lot of past agricultural plots is sell to households around cities. In a context where irrigation had become essential and had been led often collectively for example by the creation of water user associations (Associations Syndicales Autorisées, ASA), this change of belongings makes raw water available and makes fragile water balance of these associations.The experience of Gignac`s town (4000 inhabitants) located south of France demonstrates that "win-win" situations (in which everyone wins) are possible: the irrigation water network is proposed to people whose houses belong to the ASA area. This study estimates the collective welfare (namely the satisfaction felt at the same time by the households having this dual water system, by the urban water manager and the ASA) that this dual water system makes it possible to release. To evaluate the welfare, we collected urban water consumption data (years 1996-begin of 2002) and interviewed 109 household living in five districts (3 having raw water, 2 without).