How to Remove Water from Gasoline: A Comprehensive Guide

Removing Water from Fuel for Peak Performance

Have you ever tried to start your car or lawnmower only to have it sputter and stall? Chances are there was water in the gas tank causing poor engine performance. While small amounts of water won’t hurt modern fuel injection systems, larger amounts can lead to serious damage if left untreated.

Fortunately, removing water from gasoline is relatively straightforward. This comprehensive guide will teach you how to detect, remove, and prevent water in gas for optimal engine operation.

Key Takeaways:

  • Water gets into gas tanks through condensation and leaks and sinks to the bottom where it can cause corrosion.
  • Symptoms of water in gas include hard starting, engine sputtering, stalling and power loss.
  • Use a fuel filter water separator to remove water from gas. Manual draining may also be required.
  • Consider adding a fuel stabilizer or isopropyl alcohol to help disperse water.
  • Prevent future water problems by fixing leaks, keeping tanks full and using fuel stabilizers.

How Does Water Get Into Gasoline?

Before learning how to get water out of gasoline, it’s helpful to understand how it gets there in the first place. There are two main ways water ends up in your gas tank:


This is the most common cause of water contamination in gasoline. As temperatures fluctuate, condensation occurs inside partly empty fuel tanks. The water vapor condenses on the inner tank walls and drips down into the fuel.

Condensation is exacerbated by these factors:

  • Temperature fluctuations from day to night
  • Nearly empty gas tanks
  • High humidity environments
  • Short engine operation periods

Small engine equipment like lawnmowers are especially prone to condensation buildup from short run times and temperature changes between uses.


The second most common cause of water in gasoline is external leaks into the tank. Possible sources include:

  • Loose, missing or cracked filler caps
  • Rust holes in the tank
  • Cracked or disconnected fuel lines
  • Faulty fuel pump seals
  • Leaking radiator and cooling system components

As water leaks in, it gradually accumulates at the bottom of the tank where it causes the most problems.

How to Detect Water in Your Fuel Tank

Before you can eliminate water from gasoline, you’ll need to determine if water contamination is actually causing your engine problems. Here are the most common symptoms of water in gas:

Hard Starting

Excessive cranking is needed to start the engine. Water interferes with combustion, making ignition difficult.


The engine may start but then quickly sputter and stall as the fuel system tries to compress water. This happens most frequently after letting the engine sit overnight when water has time to settle into the fuel pick-up area.

Power Loss

You may experience a lack of power under load or at high RPMs as water displaces fuel volume and creates pre-ignition problems.

Increased Corrosion

Water accelerates fuel tank and fuel system corrosion leading to rusty tanks, clogged fuel filters and damaged fuel system components.

While these symptoms point to possible water contamination, visually inspecting the fuel and draining water from the tank will confirm if water is the real culprit.

Draining Water from the Fuel Tank

Once you suspect water in the fuel, it’s time to drain it. This helps dry out the tank and remove heavy accumulations from the bottom.

Follow these steps to drain water from the fuel tank:

Materials Needed:

  • Drain pan
  • Locking pliers
  • Rag

Draining Steps:

  1. Allow the engine and exhaust system to fully cool.
  2. Locate the fuel tank drain plug, typically on the bottom of the tank.
  3. Place the drain pan under the drain plug area to catch water and fuel. Wear eye protection.
  4. Use locking pliers or a wrench to slowly open the drain plug.
  5. Once fuel starts flowing, watch closely for water droplets. Allow all water and sediment to fully drain, but avoid wasting excessive fuel.
  6. When fuel runs clear with no water, close the drain plug tightly.
  7. Dispose of drained water, dry out the drain pan, and soak up any minor fuel spills.
  8. Consider adding isopropyl alcohol to help absorb residual water (see next section).

Repeat this draining process until all signs of water are gone. Draining the tank is also advisable before long-term storage.

For vehicles, regular fuel filter changes will prevent water from reaching delicate fuel injectors. Gasoline stabilizer products help emulsify water into a mixture the engine can burn.

Using Fuel Additives to Remove Water

Specialized fuel additives can also help remove water from gas and keep it suspended to prevent phase separation. Here are two options:

Isopropyl Alcohol

Adding isopropyl alcohol (rubbing alcohol) to gasoline instantly helps absorb both residual water and additional condensation. This safe solvent mixes with water and fuel to create a homogeneous solution.

Use a ratio of 25-50% isopropyl alcohol to gasoline to effectively treat water contamination. This solution can remain in the tank with no adverse effects. The alcohol will eventually evaporate.

Fuel Stabilizer

Reputable fuel stabilizer brands like STA-BIL contain powerful water dispersants that emulsify water into tiny droplets, preventing it from settling out. These polar water molecules then safely pass through the engine and exhaust system.

Adding the recommend amount of fuel stabilizer helps remove existing water contamination while providing long-term corrosion protection and fuel stabilization. Consider using stabilizers seasonally or whenever condensation is likely.

Mechanically Separating Water

In addition to tank draining and fuel additives, you can mechanically separate water from gasoline as it leaves the tank. This is accomplished using a fuel filter/water separator.

These specialized filters contain water-attracting media that draws water out of the fuel as it flows through. Separated water collects in a chamber that must be manually drained.

Fuel filter water separators provide effective mechanical removal of water without the need for tank draining or fuel additives. They are common on diesel engines and also available for gas.

Preventing Water in Gasoline

While it may not seem like a huge deal, repeatedly operating an engine with water-contaminated fuel can lead to damage over time. Here are some tips to help prevent water problems altogether:

  • Fix any fuel tank leaks immediately
  • Inspect and replace missing or cracked filler caps
  • Keep tanks at least half full to minimize condensation
  • Allow short-use small engines to fully cool before refueling
  • Add fuel stabilizer seasonally or when storing equipment
  • Install a fuel filter/water separator if water contamination is an ongoing issue

Following these fuel storage and equipment maintenance best practices will go a long way in keeping damaging water out of your gasoline, ultimately saving you money and frustration down the road.

Frequently Asked Questions

How much water in gas will cause problems?

As little as 2% water content by volume can begin contributing to hard starting and poor performance. Ideally gasoline should have no detectable water at all.

Does gasoline go bad over time?

Yes, gasoline does gradually degrade with age due to the volatile nature of the fuel. Using a reputable fuel stabilizer helps slow this oxidation process and keep fuel fresh over 12 months or longer.

What color is water in gasoline?

Water sinks to the bottom of the tank and often has a distinctive cloudy or grayish appearance when drained. It may also mix with sediment. Look for a separation layer between fuel and water.

Conclusion: Keep Your Fuel Dry for Peak Performance

In summary, water is a common fuel contaminant with potentially damaging effects including corrosion, power loss, and hard starting. Learn to recognize symptoms of water in gasoline. Regularly inspect for leaks, drain accumulated water from fuel tanks and filters, and consider fuel additives to disperse moisture. Addressing water problems quickly minimizes expensive repairs down the road and keeps your engine running smoothly.

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