A water sharing plan is a legal document prepared under the Water Management Act 2000 (WMA) in New South Wales (NSW). It establishes the rules for sharing water between the environment and entitlement holders, with the goal of simultaneously protecting water dependant ecosystems and providing certainty for water users. In NSW 49 water sharing plans have commenced to date and another 40 plans are due to be commenced within next two years covering all surface and groundwater systems. The WMA requires that due consideration be given to the socio-economic impacts of the water sharing rules during preparation and mid-term reviews of the plans. This paper presents the framework used to undertake socio-economic assessment of the impacts of water sharing rules and a case study of impact assessment. The NSW Office of Water (the Office) has used a staged methodological framework that is consistent with the socio-economic assessment guidelines for river, groundwater and water management committees developed by the Independent Advisory Committee on Socio-economic Analysis (IACSEA 1998). This framework is simple, relevant and cost effective. The case study presents socio-economic impact assessment of water sharing rules of the Coopers Creek Water Sharing Plan that commenced in 2004. The results of the case study indicate that the proposed rules could have significant negative or positive impacts on regional irrigated production and employment. This shows that proposals for environmental gains may result in substantial economic losses to the irrigators.