Taking an interest in the theme of water use on the Amerindian reservations of Arizona and more particularly in the cultural and ritual aspects, my presence evidently perturbed the local social relationships. Confronted with the systematic avoidance of American colleagues and with the refusal of the authorities of the Tohono O’odham reservation to grant me the authorization to conduct interviews on the subject of the transformation of the social uses and the symbolic practices with regard to this element, I had to rethink my fieldwork techniques and approach. This article offers feedback on these confrontational relations, which drove me to question my practices as an ethnographer. The interdiction applied to the researcher reveals the conflicts that exist between the state and Native Americans, and between members of the reservation. What are the necessary social conditions for an investigation of the access to the water and its representation ? Can Europeans successfully undertake an anthropological study of the uses of water on Indian Reservations in U.S ? This text tries to answer these questions.