Remove the air cleaner from your mower. In most cases, the cleaner has a cover that simply snaps off the cleaner housing. Removing the air cleaner gives you more room to work around the carburetor.
Locate the drain plug on the bottom of the float bowl.
Position a small container under the plug to catch the water. It is possible that the water mixed with gas and you will drain a combination of both.
Loosen the plug with an open-ended wrench and then remove the plug by turning it counterclockwise with your fingers until the water starts to flow.
Turn the plug back into the float bowl with your fingers and then give it a quarter turn with the wrench to tighten it.