Googled "lawn mower starts, sputters, and dies" worth a try?
Drain and Clean the Gas Tank. Can you Try to Run the Mower for 25 to 30 Seconds with Starter Fluid? If yes, then Do So for 3 or 4 Times and it Might Pull the Water Out of the Carburator. If it Does Not Pull the Water from the Carburator, then the Carburator will have to be Cleaned and Rebuilt.