Membrane processes are used for water treatment techniques to desalinate seawater and surface water into potable water. The undesired byproduct of these processes is a high concentrate salt. In this project, the repurposed concentrate salt was studied as a storage medium for grid-scale Thermal Energy Storage (TES). The Department of Energy’s (DOE) goal is to reduce the Levelized Cost of Energy of TES for concentrated solar power to be under 15 $/kWh by 2030. In this work, a techno-economic assessment was performed to estimate the cost of TES using concentrate salt. The total cost of TES was estimated by considering costs associated with transportation of brine, evaporation of remaining water, grinding the salt content, additives added, and containment costs while considering a positive financial gain from obtaining the concentrate from water treatment facilities. It was observed that the concentrate salt that went through solid to liquid phase change provides an increase in energy density and a reduction in TES cost. The results show a financial benefit using concentrate salt as a storage medium for heat making it a feasible material to meet the Sunshot Initiative goals for TES. Depending on the source of the brine, zero liquid discharge method, and operating temperature we can observe costs as low as (−$11.10), i.e., positive revenue. The occurrence of phase change within the operating temperature of the application significantly increases the energy storage density and reduces the cost of the TES which is seen in the results for the melting scenarios.