Yes indeed still used in some large round piston engines....and is called ADI (anti-detonation injection) and is used to cool the cylinders at very high (BMEP) takeoff power settings, instead of extra fuel. Added to the fuel-air mixture by the water regulator.
In addition, some jet engines in the past used water injection to increase takeoff thrust. Some early B707's used water injection with the JT3C-6 engines....the water used was de-mineralized and generally used up with one takeoff...about 2 and a half minutes. Worked OK...but was LOUD.