A method and a system for sequestering carbon dioxide (CO.sub.2) while producing freshwater are provided. An exemplary method includes producing saline water from a saline aquifer, desalinating at least a portion of the saline water, producing freshwater and waste brine, mixing waste CO.sub.2 with the waste brine forming a brine/CO.sub.2 mixture, and injecting the brine/CO.sub.2 mixture into the saline aquifer.