Never tried it myself, so no idea how much water it would take.
I used to work with a guy who claimed that at every 100,000 mile mark, he would put a few tablespoons of water/comet or ajax cleanser mixture into each cylinder, disconnect the coil wire, and turn it over several times. Vacuumed the residue out then did an oil washdown of the cylinders, change the crank case oil and drive. Said he had half million miles on the same engine with no rebuild in his old GMC. No way to verify if it was true or not, but such an exercise would work at deglazing and potentially improving ring seal. I think it would be easier and simpler to just change the oil regularly.