The high price of desalination is often considered one of the primary obstacles to making desalinated water a viable option for irrigated agriculture. Relatively little attention has been given to how strategic planning of regional water supplies might contribute to addressing this issue, particularly in leveraging investment in desalination by wealthier sectors to support agricultural communities. The Copiapó valley in Chile has been selected as a case study to investigate this. The study illustrates using modelling how the expansion of the mining and associated investment in desalination can reduce the economic and environmental costs of supplying desalinated water to irrigators. It was observed that the reduction of costs is affected by the degree of expansion in the mining sector, the degree of expansion in the irrigated agriculture sector, and the energy market. With potential expansions, if they invest strategically in creating an optimal water supply network, the marginal costs of producing desalinated water can be reduced to between 1.09 USD/m³ and 2.53 USD/m³ depending on the energy price. This represents a reduction of 58–3%, respectively, compared to the average cost of producing desalinated water under baseline conditions where irrigated desalination is not supported. Results show that foresightful integrated water planning, which accounts for planned expansion in water demand, can result in more realistic costs of irrigating with desalinated water - although subsidy remains a likely requirement. Such integrated water planning would help bridge the gap between the price of desalinated water for irrigation practices. Furthermore, as demonstrated in this study, these practices can minimize the environmental impact of establishing a water conveyance network.