<p>Water saving management contract (WSMC) is a market-oriented water saving mechanism composed of water saving service company and water user. The tradeoff of contract period length is a traditional problem in this mechanism. Especially for water users in public institutions, the demand for social benefits makes the decision on contract period more complicated than merely considering economic benefits. This study proposes a new contract period optimization method for WSMC project in public institutions considering social benefits. Firstly, based on traditional environmental, social, and governance (ESG) evaluation method, an ESG evaluation index for WSMC project is determined. Then, an economic-social multi-objective contract period optimization model is established with ESG index-based social benefit objective, and the solution algorithm is designed. Finally, a WSMC project case in China is studied to verify the effectiveness of the proposed method. The results show that social benefits take longer contract period than economic benefits and the water conservation profits are tilting towards water saving service company. The public nature of water resources is the main reason and water users who aim to achieve water conservation (such as public institutions) are suitable for this type of contract period. The research results of this study will provide theoretical support for water users to balance economic and social benefits.</p>