What do you do if your lawn mower got wet?

Try starting the lawn mower's engine. If the engine's not that wet, it might start after a few tries. If it does start, it's best to leave the engine running for a few minutes. The heat the engine produces will dry the internal parts of the engine. Is it not starting? Continue to step 2. Not sure how to start the lawn mower? First read this article:

If the lawn mower won't start, dry the parts of your lawn mower. Dry the outside of the lawn mower with a cloth and then remove the spark plug. The spark plug is located at the back of the engine. Dry and clean it. Then, remove the air filter and check if it's wet. Before you replace it or put it back in, have a look at the carburetor first. If necessary, spray starting fluid into the air inlet behind the air filter you just removed, so that the carburetor starts properly. Put the air filter back in when it's dry.

If the last 2 steps didn't work, check if any water got into the gasoline. Water is heavier than gasoline, so it'll gather on the bottom of the tank. Take the gasoline out of the lawn mower and collect it in a jerrycan. Let the gas tank dry. The lawn mower has a small container between the gasoline tank and the engine, to collect the water. Empty the container. Replace the fuel filter, if your lawn mower has one. Next, fill the gas tank with new gasoline.

After you've checked the gasoline, check the oil. If it looks milky, it contains water. Drain the oil from the lawn mower, then fill the mower with new oil. It's important to replace the oil, since water in the oil will affect the engine's performance because it's not being lubricated properly.