The worldwide demand for new concrete buildings is increasing at a rapid pace to keep up with urban development. Despite the need, concrete production and its use have a number of environmental consequences. The production of concrete creates a substantial need for water that directly causes a burden on the already scare natural resource. In United Arab Emirates the majority of the water used for concrete production is obtained through desalination of the seawater. Desalination of seawater produces highly saline wastewater commonly known as reject brine or concentrated brine that has numerous negative environmental effects. The production of cement, the primary ingredient in the production of concrete is responsible for the generation of nearly 5% of the global carbon dioxide that is a potent greenhouse gas. With the intent of reducing the carbon footprint of concrete production, a study was carried out to determine the effect of using reject brine as the source of water and the use of ground granulated blast furnace slag (GGBS) as a replacement for cement. Concrete samples having three different cement contents were prepared with normal tap water and reject brine. Results showed that the use of GGBS and reject brine improved the strength of concrete produced by 16.5%. Replacing 50% of the cement with GGBS and using reject brine as the source of water has a potential for reducing 176 kg CO2 and 1.7–3.4 kg of CO2 equivalents per one cubic meter of concrete, respectively. The use of the waste reject brine can potentially save USD 170–340 per cubic meter of concrete produced.