Pontoon with water in gas

I took this Lowes Pontoon to the shop because it spit sputtered then died and would not start again. They replace the fuel module and stated there was water in the gas. They said they drained the tank. Got the boat out of the shop and it sat for 2 months before we went and filled the tank up and put it on the water again. As we made it out of the no wake zone and gave it throttle, it started spitting and sputtering again. Took it back to same shop and they said it had 3-5 gallons of water in the gas tank. Drained it, put more gas in and took it from shop to lake. Runs perfect. How is this water getting in the gas tank? The shop has done a good job so far and suggest we take it to a Lowes dealer and let them determine a fix. Any ideals?

Where is the vent for the tank located? Water could be spraying in it.

Gas cap is the vent.

but worth a look to see if there is a vent hidden where the tank tucks under the floor deck

Quite using fuel with ethanol . Look up Phase Separation . Ethanol attracts water and when it reaches its saturation point all the ethanol and water separates from the fuel . Its good business for the boat repair shops . Too bad they weren't more honest and warned you what a nightmare ethanol is for equipment that sits for awhile in between uses . The only thing ethanol is reasonably safe in is vehicles that get used regularly and always get fresh fuel .

My Mom and Dad had the issue with getting water in the fuel on their pontoon boat. The fuel tank gas cap vent allowed water to get in the way it was made. I found that an aerosol paint can cap fit over the gas cap perfectly, it popped on and off for fueling and kept the water out! Might try it.