CO2 flooding is an environmentally friendly and cost-effective EOR technique that can be used to unlock residual oil from oil reservoirs. Smart water is any water that is engineered by manipulating the ionic composition, regardless of the resulting salinity of the water. One CO2 flooding mechanism is wettability alteration, which meets with the main smart water flooding function. Injecting CO2 alone raise an early breakthrough and gravity override problems, which have already been solved using water alternating gas (WAG) using regular water. WAG is an emerging enhanced oil recovery process designed to enhance sweep efficiency during gas flooding. In this study, we propose a new method to improve oil recovery via synergistically smart seawater with CO2. This new method takes advantage of the relative strengths of both processes. We hypothesized that SW depleted in NaCl provided more oil recovery. We also added that depleting NaCl in seawater is not the end of the story; diluting divalent cations/anions in the seawater depleted in NaCl provides higher oil recovery. Injecting smart seawater depleted in NaCl with diluted Ca2+ and CO2 resulted in a high oil recovery percentage among the other scenarios. Thus, the above water design was applied as a WAG in three cycles, which resulted in a much higher oil recovery of 24.5% of the OOIP. This improved heavy oil recovery is a surprising and promising percentage. The spontaneous imbibition agreed with the oil recovery results. This study sheds light on how manipulating ions in the water used in WAG can significantly enhance oil recovery.