30 years ago I got to see first hand a brilliant inventor/marketer, Rudy Gunnerman, try to combust water. If I remember right he was the inventor of the wood pellet in the 60's - which of course did revolutionize the wood burning stove industry - and gave him some credibility.
At that time I worked for the US distributor of a german car manufacturer and they provided Rudy with a Porsche 944 to run on the dyno with his gas-water (85/15) mixture. Rudy had all the claims (especially touted his "surfactant") and supposedly drove in with a car running on the mixture. 944 engine died on the dyno...
Several years later I was working for a Cat dealer and in walks Rudy and some gold mine managers - Rudy was now mixing his water with diesel and getting "amazing results" - so it was now a Cat 3512 haul truck engine to be placed on the dyno. Good results - the engine ran - power increased by a small amount - and then went down somewhat commensurate with the amount of water in the fuel - not a scientific study on the dyno and they then tested several trucks at the mine.
What one engineer stated is that the water in the diesel turned to vapor and "steam cleaned" the engine internally and maybe provided improved combustion for a short time - anyway the experiments/testing died shortly after that when the trucks had "no power."
After that, Rudy then mixed diesel with natural gas and had some success with on-highway trucks. He died several years ago but his son carried it forward - they called it GDiesel (lots of Google info) but it went bankrupt several years ago.
After all that I saw, I do believe that there aren't too many BTU's in water - even salt water - but I do have cow magnets on my fuel lines.