Résumé
When the water supply available in a given river basin is insufficient to cater to the needs of its population, users usually devise individual and collective responses to water scarcity. Generally, this leads to more reuse of water along the river system, with little water being lost out of the basin, and leads to reallocation of resources. This paper recounts the development of the Chao Phraya river basin over the second half of last century and shows how supply and demand have evolved in parallel and how changes and innovations have emerged in response to growing imbalances. Various adjustments have been made in agricultural practices and significant changes have affected efficiency, water management, institutions, and policy making. These changes appear to be driven not only by planned state interventions and policies but also by local actors. The paper provides an example of dynamic reading of the water status in a basin and shows that the concepts of supply and demand need to be qualified to better understand how short- and long-term changes are linked to imbalances between the two terms. The study suggests that the scope for achieving water savings and/or economic gains by demand management is far more limited than is commonly assumed and that potential reform benefits will be rather in terms of equity and better service through users' empowerment.