Check the containers that you are using for residual water at the bottom. If you live in a humid area, you might get condensation inside the tank. If that is the source of the moisture, then fill the tank when you are finished using the tractor, and always keep your storage containers tightly sealed. If you suspect the fuel cap, put a piece of Saran Wrap under the cap before you put the cap back on during storage. You will need to remove it before using the tractor so the tank can breathe. Last thought it might be one of your neighbors putting water into the fuel tank for some perceived misdeed you might have done in the past. I hope that isn't likely, but I know it happened before.
