Evaluation of value of irrigation water is essential for supporting policy decision making relating to investments in the irrigation sector, efficient allocation of irrigation water and water pricing and for crafting policies to compare the variable impacts of water reform within and across sectors of the economy. This paper asks the question of how much an established irrigator would pay for water and at what price farmers planning to expand the area they have under irrigation would consider paying for the right to access water. An analytical framework is developed to estimate the net present value of both annual and perennial agricultural activities in the Murrumbidgee catchment. Using these estimates the total value of water used in Murrumbidgee catchment is estimated. An aggregate water supply curve is derived for the catchment from where water may be acquired from irrigators for environmental flows. © 2010 The Author. Journal compilation © 2010 Australian Agricultural and Resource Economics Society Inc. and Blackwell Publishing Asia Pty Ltd.