Although there is good evidence that irrigation played an important role in Roman agriculture, it has so far received too little attention. This paper seeks to address the subject of its funding at different scales. Among the different choices landholders had to make, investments in hydraulic infrastructure were guided by their particular needs for cultivation and breeding, the environmental context, and the management of a natural and sometimes limited resource. The attention is here turned towards the financial, human, and material nature of the investment required. The cross-reading of archaeological sources with literary and legal texts shows that the costs of irrigation in single estates varied according to the technical constraints (length and construction of the conduit, necessity to store water, etc.), but the efforts made to invest also reflect the profits expected. A key element concerning investments towards irrigation, in any case, lies in the access to water. In that respect, Roman law played an essential role through servitude rights.