Watershed management deals with managing groundwater and drinking water in dryland areas. In this study, a dynamic optimisation model for sustainable agriculture and watershed management is developed, which can help farmers in dryland regions maximise their profit from agricultural production. The steady-state values of water stock, profit and allocation of land between highly water-intensive and less water-intensive crops are determined. This study also carries out sensitivity analysis by perturbing various parameters such as technologies used in crop production, discount rate and annual recharge of groundwater stock. The results show that as the technology used for less water-intensive crops improves, groundwater stock and profit increase. This study captures how upstream and downstream farmers can optimise their net benefit from agriculture when there is water conflict between them. It also demonstrates how their water extraction patterns and benefits can change in the presence and absence of a social planner.