1. Why is there water: The engine burns oil, and the emissions must be water and carbon dioxide. Water is in the form of high-temperature steam when it is started, and becomes water after cooling.
2. Replace the oxygen sensor: why should it be replaced? Turning on the light just tells you this problem. Even if this sometimes breaks, you can still burn it with acetylene gas - it's possible to salvage it, not to mention that yours isn't broken yet. It would cost more than a hundred to replace it, which is a waste.
3. Water cannot be discharged: Is the exhaust pipe blocked or the drainage hole of the exhaust pipe blocked?
4. Question of concern: Is your water tank short of water? I ask this because I'm worried that if your cylinder bed is flushed, it will be a bit troublesome. How to read columns? Check the four connecting parts of the engine to see if there are any traces of fluid leakage.