If you live in an area with gasoline contamination in your groundwater, you may be wondering if a reverse osmosis (RO) system can remove it.
Gasoline is a mixture of hundreds of different chemicals. Reverse osmosis can remove many of these compounds, but the degree of removal depends on the size and solubility of each individual compound.
For example, RO can remove up to 98% of benzene, a known carcinogen, from water. However, other compounds present in gasoline, are more difficult to remove.
Reverse osmosis systems generally include a carbon pre-filter, and activated carbon is a very effective way to remove gasoline from water. This combination of reverse osmosis and carbon adsorption provides two methods of treating your water. The carbon filter will remove any remaining pollutants if the RO membrane is unable to remove all of the gasoline compounds from your water.
As you can see, this is a complicated issue. In this blog post, we will answer the question of how well reverse osmosis can remove gasoline from water and a whole lot more.
Gasoline
Gasoline is a liquid petroleum product that is used as a fuel for internal combustion engines. It consists of hydrocarbons and is typically mixed with other chemicals to improve its performance. Gasoline is flammable and can be toxic if inhaled.
Many communities have gasoline in their drinking water as a result of leaking underground storage tanks or spills from gas stations. Gasoline can contaminate your drinking water and make it unsafe to consume. If your water supply is contaminated with this fuel, you will need to take steps to remove it before using the water.
What’s in gasoline?
Gasoline is not a single chemical. It’s made up of about 150 different compounds, including:
- butane
- pentane
- isopentane
- benzene
- ethylbenzene
- toluene
- xylenes
Gasoline also has additives like lubricants, rust inhibitors, and anti-icing agents to improve its performance.
Health risks of gasoline
Gasoline is a mixture of many substances, including volatile organic compounds (VOCs). VOCs can cause cancer, liver damage, and kidney damage. They can also irritate your skin, eyes, and throat. Gasoline is also flammable, so it poses a fire risk.
Drinking water contaminated with gasoline can cause a range of short- and long-term health effects, including:
- Cancer
- Liver damage
- Kidney damage
- Skin irritation
- Eye irritation
- Throat irritation
- Nerve damage
- Dizziness
- Headaches
- Nausea
- Vomiting
- Diarrhea
Some of the specific chemicals in gasoline that are especially problematic are:
- Benzene – a known human carcinogen that also increases the risk of leukemia, anemia, chromosome damage, and other illnesses.
- Toluene: can cause nerve damage, inflammation of the skin, and liver and kidney damage.
- Ethylbenzene: exposure results in throat and eye irritation, chest constriction, and neurological effects such as dizziness.
- Xylenes: can irritate the eyes, nose, skin, and throat. It also causes headaches, loss of muscle coordination, and in high doses, death.
- MTBE: is a suspected carcinogen that also effects the liver and kidneys and causes headaches and throat irritation.
How does gasoline get into my water?
Gasoline gets into water through leaking underground storage tanks, gas station spills, and other sources. Once released, it can find its way into drinking water supplies.
Surface spills can find their way to rivers, lakes, and streams by flowing through stormwater systems or directly over land. Subsurface releases can contaminate groundwater, which is the water supply for about half of Americans.
Reverse Osmosis
Reverse osmosis is a widely used treatment method that reliably removes a wide range of contaminants from drinking water. It is effective at reducing the concentration of impurities such as lead, PFAS, and heavy metals
How RO works
Reverse osmosis systems use a semipermeable membrane to remove impurities from water. The membrane allows water to flow through while trapping dissolved solids and other contaminants. The system applies pressure to the water, forcing it through the membrane and removing any impurities.
The membrane is constructed of a semi-permeable polymer that is spirally wrapped around a central tube. The water is forced through the membrane, and the impurities are filtered out. The clean water is then collected on the other side of the membrane, while the contaminants are retained in a concentrated brine. This brine waste is then flushed down the drain.
Reverse osmosis systems can be used to treat both municipal water supplies and private wells. They are effective at removing a wide range of contaminants, including lead, bacteria, viruses, pesticides, and more.
RO system components
Reverse osmosis systems typically consist of three modules:
- pretreatment
- reverse osmosis membrane
- post-filter
Pretreatment protects the membrane from fouling and damage caused by chlorine. It usually consists of a sediment filter and an activated carbon filter. The sediment filter removes particles such as dirt and rust, while the activated carbon filter removes chlorine and other chemicals.
The reverse osmosis membrane is the heart of the system. It’s a thin film composite (TFC) that remove contaminants from water. The TFC is made of several layers of material, including a semi-permeable membrane.
The post-filter is a final stage of filtration that removes any remaining impurities from the water. This is typically a second carbon filter that ensures the water is safe to drink and tastes great.
Some RO systems include a water storage tank, which stores the clean water until you’re ready to use it. This is desirable because the flow rate through the filter is slow. Having a storage tank ensures you can fill a glass or a cooking pot quickly with clean water without having to wait.
Reverse Osmosis and Gasoline Treatment
Gasoline is a complex mixture of many petroleum hydrocarbons. Some of these hydrocarbons, like benzene and toluene, are more difficult to remove than others.
How well does reverse osmosis remove gasoline
Reverse osmosis has a mixed performance when it comes to removing gasoline from water. It removes some of the components of gasoline very well but only moderately well for others.
RO can remove most of the large molecules in gasoline as well as the heavy hydrocarbon compounds.
Compounds such as benzene, toluene, ethylbenzene, xylenes are only partially removed with RO filtration.
This table summarizes the removal efficiency of reverse osmosis and some of the major components of gasoline.
| Gasoline Constituent | RO Effectiveness | Removal Rate |
| Benzene | Moderate | 55-98% |
| Ethylbenzene | Moderate | 60-95% |
| Toluene | Moderate | 60-95% |
| Xylenes | Moderate | 60-95% |
| MTBE | Good | 85-98% |
Carbon pre-filter and RO systems
Virtually every reverse osmosis system includes an activated carbon pre-filter. This filter is intended to remove chlorine to protect the membrane from damage. Activated carbon is a very effective treatment method for gasoline and many of its constituents. This includes benzene, toluene, ethylbenzene, xylenes, and MTBE.
Challenges with gasoline and RO filtration
The membrane of reverse osmosis filters is made of a semi-porous polymer. Many of the VOCs and solvents that make up gasoline can damage this membrane, leading to a reduction in its ability to remove contaminants. This also reduces the lifespan of the membrane.
As noted above, RO systems include an activated carbon pre-filter that can remove these compounds. However, the activated carbon filter will need to be replaced more frequently if it is treating water that contains a high concentration of gasoline.
RO membrane type matters
The type of membrane used in the reverse osmosis system has a large effect on how well it can remove gasoline. There are several types of membranes that can be used, each with its own advantages and disadvantages. These include:
- cellulose acetate (CA)
- thin film composite (TFC)
The thin-film composite membranes are the most effective at removing contaminants like benzene and toluene. The cellulose acetate membrane, however, is more resistant to degradation from solvents and chlorine.
Factors to Consider with Reverse Osmosis
If you’re concerned about the quality of your drinking water, a reverse osmosis filter may be a good option for you. RO filters are able to remove a variety of contaminants from your water, including lead, mercury, and chlorine. However, there are a few factors you should consider.
Installation cost of reverse osmosis
Depending on your home’s plumbing, installing an RO system can be relatively simple or quite complex. If your home has a standard under-sink configuration, you can likely install the filter yourself. However, if your home has multiple faucets or you need to drill new holes for the filter, it’s best to hire a professional.
A whole-house RO system can be expensive to install, especially if you have to modify your home’s plumbing. An under-sink unit, on the other hand, can often be installed by a good do-it-yourselfer for a reasonable cost. Each home is unique, so you’ll have to determine which system is right for you.
Maintenance cost
RO filters have sediment filters and activated carbon filters that have to be replaced. A sediment filter will usually last for about six months before it needs to be replaced. Carbon filters have to be replaced every 3 to 6 months, depending on how much water you use and the amount of chlorine in your water.
The cost of replacement filters can vary, but you can expect to spend around $60 to as much as $200 per year on them. Whole house filters are 3 to 4 times as much as under-sink filters.
While this may seem like a lot, it’s important to remember that RO filters can remove a variety of contaminants from your water, making it safer and healthier to drink.
Whole-house versus under-sink units
Another thing to consider is how much water you’ll need to filter. RO filters are typically sized according to the number of gallons they can process per day. If you have a large family or use a lot of water for cooking and bathing, you may need a larger filter.
Reverse osmosis systems are available in a wide range of sizes, from small countertop units to large industrial systems. They can be used for point-of-use (POU) applications, such as filtering water for a kitchen sink, or point-of-entry (POE) applications, such as filtering all the water coming into your home.
Deciding which type of RO system is right for you depends on a number of factors, including your budget, the size of your home, and your water quality. Read my article on under-sink RO systems and whole-house RO systems for a detailed explanation.
NSF certification
Reverse osmosis filter manufacturers often make claims about how well their units remove contaminants. The best way to be certain of their claims is to look for units that have been certified by NSF International.
NSF is an independent organization that tests and certifies products to ensure they meet strict standards for quality and safety. If a product has been certified by NSF, you can be confident it will perform as advertised.
The applicable standard for point-of-use reverse osmosis systems is NSF/ANSI 58. It covers the following parameters:
- Materials of construction and leaching of harmful substances
- Mechanical integrity
- Removal of total dissolved solids (TDS)
- Efficiency rating
- Recovery rating
- Contaminant concentration reduction
Conclusion
Reverse osmosis is a water filtration method that has a mixed performance when it comes to removing gasoline from drinking water. It removes some of the components of gasoline very well but only moderately well for others. Although reverse osmosis can remove most of the large molecules in gasoline, it does not do as well with smaller molecules like benzene and toluene.
Activated carbon filters are effective at removing many of the compounds that make up gasoline, including benzene, toluene, ethylbenzene, xylenes, and MTBE. However, these filters will need to be replaced more frequently if they are treating water that contains a high concentration of gasoline.