The commercial pilot had refueled and reloaded chemical and departed the airport en route to his third spray mission of the day when the aircraft lost power. The pilot selected an open field next to the cane field that he intended to spray and set up for his forced landing. When the airplane touched down the wheels sank into the mud and nosed over coming to rest inverted. The pilot was uninjured. The airplane sustained substantial damage to the wings and wing struts. The pilot stated in the pilot operator report that water was found in the fuel resupply truck and in the airplane fuel tanks.