Regulation of a water resource system is one of the challenging tasks due to uncertainty involved in demand and supply. It may be due to changes in the climatic conditions, living standards of people, land-use patterns and even because of changes in technology. The problem becomes even more complicated if the objectives pertaining to demand and supply are multiple and conflicting in nature. Therefore, this paper deals with regulation of water resources system based on "if-then" fuzzy logic-based rules which interlinks concepts of interpolative reasoning, logical implications and certain inference tools to infer knowledge about a water resource system using linguistic descriptions. Reasonable inferences have been drawn using concept of tautologies viz. modulus ponens and modulus tollens. Finally, the model is applied to a practical case study in order to demonstrate effectiveness of the proposed logic. The main motive of this study is to demonstrate applicability of fuzzy inference system for regulating operations of water resource systems.