The discussion centers on the controversial method of using water to decarbonize car engines by introducing it into the intake while the engine is running. Proponents claim that water turns to steam upon contact with hot engine components, helping to dislodge carbon deposits, a theory supported by observations of clean pistons in engines with failed head gaskets. However, skepticism exists regarding the effectiveness of this method, as it primarily addresses carbon buildup in the combustion chamber rather than in the intake system where most deposits accumulate. Historical practices, such as steam injection in the 1970s, are mentioned, but concerns about practicality and potential risks, like hydrolocking, are also raised. Overall, while water may assist in cleaning some engine parts, it is not a comprehensive solution for carbon buildup.