Here’s a shiny new syphon breaker in the engine cooling line before the water is injected into the exhaust system. Most yachts have them, and they don’t last for ever. It’s there for a good reason, and if it fails, an engine-full of water may result. It costs nothing to inspect it every year and clean its valve. If in doubt, it won’t break the bank to replace it, then sleep easy all night long.