The electric arc furnace (EAF) slag could be exploited in several fields of application, such as land filling, road constructions and concrete production. However, their use is limited by the presence of polluting chemical elements (chromium (Cr), barium (Ba), Vanadium(V), etc.) that can be dangerous to humans and the environment. Thus, chemical and structural stability is a fundamental requirement, especially when the slag may come in contact with water. Therefore, the interaction between slag and water is key, in order to classify the slag as a safe raw material. In this work, the effect of slag chemical composition on the chemical leaching of about seventy EAF carbon steel slags of different production steel grades was investigated. Standard leaching tests (24 h at 10 l/kg) in deionized water on slag bulks were performed and the results were correlated with the slag chemical composition. The survey has made possible defining the safe chemical composition areas on the main ternary diagrams, able to transfer stability to the slag. The results obtained indicate the water/slag ratio as the most important factor in the release of polluting substances, also identifying a critical scenario for slag recycling.