In this paper we consider both hydrology and governance as critical dimensions for irrigation water security. We scale down the overall water security concept to the agricultural sector, suggest an index of irrigation water security faced by farmers, and provide an empirical illustration in the case of Tajikistan. Irrigation water security is investigated by three different dimensions: (a) a hydrology dimension, expressing a lack of water availability; (b) a governance dimension, the perceived difficulty in accessing water; and (c) a hybrid dimension of governance and hydrology. We developed an irrigation water security index, which we empirically tested using farm household survey data (N = 399). This index provides evidence that different farm types, e.g., small versus large, perceive different water security threats. Further, we found that if one dimension is less distinctive, the complementary dimension occurs as a coping mechanism. Thus, we conclude that diversified support mechanisms for infrastructure and management are needed to reach a higher level of water security.