Water presents significant advantages when used in heterogeneous catalysis. Unlike traditional organic solvents, water is non-toxic, non-flammable, and readily available. Heterogeneous catalysts, which differ in state from the reaction medium, can be performed in water to facilitate various chemical reactions. For instance, micellar catalysis has proven effective for aminations, leveraging recyclable catalysts and aqueous reaction media to achieve high reactions yields of pharmaceutical APIs and complex targets. Another example of heterogeneous catalysis is magnetic nanocatalysis which has shown promise for the reduction of nitroaromatics in aqueous media, demonstrating catalyst magnetic retrievability and efficiency across multiple cycles for the synthesis of pharmaceuticals, polymers, pesticides, and cosmetics. In general, the use of water not only helps improving the safety and efficiency of these type of reactions but also allows for catalyst reusability, thereby reducing waste and production costs. However, challenges such as reactivity issues, solubility limitations, and operational constraints must be addressed as well. Overall, the integration of water as a solvent in heterogeneous catalysis aligns with green chemistry principles, promoting cleaner and greener processes.