How to Get Water Out of Your Boat Gas Tank

Learning how to get and keep water out of your boat gas tank will extend the life of your engines and ensure your gas stays usable longer.

Accidents happen. Maybe you’ve left the tank open, had to refill your tank during bad weather, or dropped your fuel cap in the water. Or maybe you just looked into your gas tank and noticed rust. Some water will inevitably get into gas. The enemy of fuel is water. They say water and oil don’t mix, but they kind of do. Water is always trying to find its way into your fuel. The moisture in the air, condensation, etc. Water dilutes your fuel. When the VOCs evaporate and your fuel has too much water in it, it becomes stale and doesn’t work as well. Too much water in the fuel can also damage your engine as well.

This isn’t to say that gas can never have any water in it. Gas stations are allowed to have so much water in their tanks anyway. Gas Stations pull pump reports nightly to make sure they aren’t in excess of allowance. Obviously, water isn’t added to the tanks, but it builds up just like anything from condensation, leakage, rain etc, just as a you would out on the water boating or trolling.

Remove all Liquids From the Tank

The easiest and best way to get the water out of the tank is to have no liquids in the tank. Siphon out the water with the gas and start over with fresh gas. If there isn’t too much water in it, you can use the old stale gas bit by bit by mixing it with fresh gas when you refill your tank, especially if you mix it with a high octane.

Mix the old work the new if it’s not for to much water in it. Otherwise you’ve got yourself some fire starter. Pull out the old siphon and get to work. If you’re still using a hose and sucking gas, please get yourself a real siphon. You’ll thank me. I fought against it for the longest time, but its not that expensive and its great to have.

Pro XL Siphon

Preventing Water From Getting In Your Gas Tank

The best thing you can do to keep water from getting in your gas tank is to leave the gas cap on the tank while you’re on the water as much as possible. I realize that a “thanks captain obvious” answer, but still the truth. If you find that your gas regularly collects condensation, try to keep your gas tank at 100%. By constantly refilling you’ll be adding more good clean fuel to your boat gas tank, helping to keep the gas to water ratio at a low level. Additionally, there will be less gas tank wall space for condensation to accumulate on. Also, inspect the gasket on your fuel cap, and make sure there are no other leaks where moisture could get in.

The best thing to do is use ethanol free gas. Ethanol gas actually accumulates water as it sits more than ethanol free gas according to some sources. You’ll also want to consider using a fuel additive like Stabil or Sea Foam. I’m a Sea Foam guy myself. I consider it the magic juice that can fix almost any engine problem. I used to buy it from Walmart, but found recently that Amazon was consistently beating their prices.

Seafoam Motor Treatment

Water Separating Fuel Filter

This is the most effective way of keeping water out of your boat’s engine, but this is more of a permanent type of solution. A water separating fuel filter pulls the water out of the gas, storing it in a reservoir that you can drain when it gets full. It’s not super expensive, but it can be a little bulky. If you’ve gotten water in your fuel once in the last 5 years, I probably wouldn’t get one of these. However, if you live somewhere humid, and having high water content in your fuel is a regular event, having a fuel filter that separates the water is a must.

This fuel filter is a universal fit fuel filter, and is designed specifically for boating applications. There is a drain screw that allows you to empty the water and debris that the filter removes from your gas. It’s extremely effective, and has a 4.8 star average review on Amazon. It’s our go to.

SeaSense Universal Water Separating Fuel Filter

If you need to clean off rust from inside your boat’s gas tank, this video below is a very helpful resource.