I'm not sure if this is what you are asking, but a chemical reaction that happens in water or that uses water as one of its solvents is called an aqueous solution.
Your question isn't very clear because based on 'another substance' it could refer to anything but usually if you are referring to a mix with water it would be an aqueous solution
Your question isn't completely clear as there are many possible answers but i think you might be talking about an aqueous solution
Electroysis. When you pass electricity through water, it decomposes to produce two gaseous elements, oxygen and carbon dioxide. It has a reactant and also a product formed after the reaction.
I think the answer you are looking for is hydrolisis.