Chances are, no one is intentionally adding water to your fill-up. However, there could be many other ingredients in there.
Are You Buying Watered Down Gas?
Published on Apr. 03, 2025
The other day, someone shared with my editor a conspiracy theory about the gas station down the road watering down their product. My editor, being naturally curious, wanted to get to the bottom of the tale. What she quickly learned is that a lot of other people are Googling this very question. The short answer is no — businesses do not “water down” their gasoline with water. However, a lot of the gas we buy contains various additives.
“Today’s fuel is altered in a way that it can have a great impact on your vehicle’s performance and durability,” says Alan Gelfand, owner of German Car Depot. “With years of experience working on high-performance vehicles, I know too well how the right fuel can add years to your engine’s life, and how the wrong one can reduce it to a frame.”
Here’s what to know about gas additives, and how they affect your vehicle.
Do Gas Stations Add Water to Gas?
No, gas stations do not add water to gas, especially because water does not burn or mix well with fuel. Still, water may unintentionally end up in gas due to condensation or leaks in the underground tanks, and that can damage your engine.
Can Gas Be Diluted With Other Additives?
Yes, gas is often diluted with other additives, most of which are aimed at enhancing your vehicle’s performance.
“In fact, the best gas for your vehicle has additives,” says Melanie Musson, an auto industry expert with Autoinsurance.org. “For example, cars that use only gas from Top Tier stations have better performance and reliability than cars that use gas that doesn’t have the additives.” (Top Tier gas stations sell gas that exceeds EPA minimums on quality.)
The exception to this is the gas additive ethanol, says Chris “Moose” Pyle, a master-certified technician with JustAnswer. “Ethanol does not make as much power as gasoline, so even though it is a tad cheaper to buy, you get fewer miles per tank, so the benefits are not really there,” he says.
How Do Additives Impact Gas Quality?
“They impact it big time,” says Alex Black of EpicVIN. “Good additives maintain your engine, keeping it clean and running smoothly, and even improve mileage by a little. Bad or missing additives cause deposits and reduce performance.”
One of the most common yet potentially problematic gas additives is ethanol. “Not all cars, boats and small engines can use high levels of ethanol,” says Pyle.
What Additives Are Added to Gas?
Ethanol
The overwhelming amount of gas sold in America is up to 10% ethanol. “It is a cleaner-burning fuel that decreases emissions and stretches fuel supplies, but it is also a moisture absorber, so it can destroy older engines, boats and smaller equipment like lawnmowers,” says Black.
How ethanol impacts gas quality: It lowers energy content (and therefore overall MPG) and can create fuel system issues in some vehicles. “You can actually test the fuel at home with a beaker to see the percentage of ethanol in your fuel,” says Pyle. “It is very quick and easy, and a fun project and learning experience.”
Detergents
Detergents remove carbon deposits from intake valves and injectors, helping your engine stay clean and improving gas mileage and long-term performance. Most Top Tier gas stations add these.
How detergents impact gas quality: Using high doses may sometimes compromise lubrication.
Corrosion Inhibitors
Corrosion inhibitors help keep prevent corrosion in the fuel system, which in turn helps the system last longer. They’re especially helpful for vehicles that are seldom used or used in humid conditions. They are also good for counteracting the moisture attracted by ethanol blends.
How corrosion inhibitors impact gas quality: Black says keeping your fuel system free of rust helps keep your gas cleaner.
Octane Boosters
Octane boosters, like Toluene, prevent knocking and improve performance, especially in high-performance and turbocharged engines and other vehicles that require premium gas.
How octane boosters impact gas quality: On the negative side, some compounds like MMT, a gasoline octane enhancer, can harm spark plugs and sensors over time, says Gelfand.
Lubricants
Lubricants help keep the moving parts of an engine running smoothly. “The ethanol has a tendency to dry out things to some extent, and these keep fuel system parts and seals lubricated,” says Black.
How lubricants impact gas quality: They help preserve rubber and plastic parts, especially on older engines.
Fuel Stabilizers
Fuel stabilizers are good for cars and boats that are in storage or tend to sit around for a month or two at a time because they slow down fuel breakdown, so the gas will remain viable for a longer period.
Demulsifiers
These keep water and gas separated and make it easier to filter out water before it enters your engine. How demulsifiers impact gas quality: They help avoid stalling or engine ruin resulting from water-contaminated fuel, says Black.
Fragrance Additives
These are used infrequently in certain boutique or racing fuels and don’t impact performance too much since they only change the smell of the exhaust.
Cold Flow Additives
These help keep diesel fuel in liquid form during cold weather so engines can function during below-freezing conditions.
Dyes Off-road diesel fuel contains red dye, so it can be monitored for tax purposes and to signify that it’s illegal for on-road use. The dyes do not impact gas quality.
FAQ
What additives does each gas station use?
What brand of fuel you buy can make a difference in your car’s performance and longevity.
“Gas stations that sell fuel cheap or fuel at a discount are usually giving you the most basic fuel,” says Pyle. “It is still good fuel and meets the requirements of the law, but may not have additives to help for winter use, nor additives to help clean the fuel system.”
Conversely, Top Tier stations add various additives that are beneficial for your car. For example;
- Shell uses “nitrogen-enriched” detergents to improve the flow of the fuel.
- Chevron’s Techron is widely known for its ability to prevent rust and is recommended for use to avoid clogging of the engines, says Gelfand.
- Costco is top-of-the-line certified with a high level of detergents. “Interestingly, Costco uses Top Tier gasoline from other refineries, so the gas at Costco may be exactly the same as the fuel from ExxonMobil, Shell and so on, depending on the location and contract,” says Musson.
- BP has “Invigorate” technology to prevent deposit formation in the fuel injectors.
- ExxonMobil’s Synergy additives claim to enhance mileage.
“As for the drivers of German cars, I would suggest using premium fuels with good detergent treatment from good gas stations,” says Gelfand. “Your engine is a delicately constructed unit; therefore, it is important to use the right fuel for your car as opposed to thinking all fuel is the same.”
About the Experts
- Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience. He has also worked as an expert for JustAnswer, the expert on-demand platform, since 2006.
- Alan Gelfand is owner of German Car Depot, an independent automotive service center in Hollywood, Florida, which specializes in the service and repair of German vehicles.
- Melanie Musson is an auto industry expert with Autoinsurance.org, where she has worked for nearly a decade.
- Alex Black is chief marketing officer at EpicVIN. He has been car expert for more than 15 years, working at car auctions, vehicle history providers and more.
