As for piston engines, on the P&W 2800 CB series engines, water injection was very necessary and very effective. At dry power, we'd produce 1950 horsepower per engine, when we did a wet takeoff, we gained 450 horsepower per engine. On a DC-6, we would gain 1800 horsepower on a wet take off, and we needed it too! I have vivid memories of takeing off from Miami International and going threw downtown Miami, 12 miles away, looking UP at the tops of the buildings. It would take 30 minutes to get to 9000 feet!
As for serviceing, not a big deal.