Résumé
The French Water Law of 2006 requires the establishment of local organisms for irrigation water management, in charge of sharing water among farmers. This raises questions of designing a decentralized water management. Two economic tools are designed here to comply with Ostrom's design principles (1990): a payment-and-penalty mechanism, and a system of nested self-regulation. Through a participative and foresight approach, these tools have been discussed by three groups of farmers and institutional representatives in the Clain river basin (Western France). The former was unpopular for participants, who rejected the 'carrot and stick' principle. The latter has been appreciated, even judged as a possible future.