9 Contaminants a Reverse Osmosis System Can Help Remove From Drinking Water

ks2381

Aug 31

10 min read

A glass of clear tap water can still contain substances you can't see, taste, or smell. Did you know the Los Angeles Department of Water and Power reported that arsenic was detected in the city's drinking water in 2025, with the highest measured level at 7.0 µg/L? The reported levels remained within applicable drinking water standards, but the finding demonstrates that treated municipal water can still contain measurable contaminants.

Arsenic is only one concern. Depending on the water source and local conditions, homeowners may also have questions about lead, fluoride, PFAS, chlorine, heavy metals, and dissolved solids. Many of these substances cannot be detected by simply looking at or tasting water, which is why some Los Angeles homeowners consider additional filtration for the water they drink and use for cooking.

A Reverse Osmosis System can provide that additional layer of treatment at the point of use. By pushing water through a semipermeable membrane as part of a multi-stage filtration process, reverse osmosis can help reduce a range of dissolved contaminants. Understanding what it can address can help Los Angeles homeowners choose a drinking water system based on their specific water quality concerns.

How Does a Reverse Osmosis System Work?

Reverse osmosis uses pressure to push water through a semipermeable membrane. The membrane allows water molecules to pass through while reducing many dissolved substances that are larger than water molecules or otherwise rejected by the membrane. The treated water is collected separately from the concentrated water containing the rejected contaminants.

A complete reverse osmosis water filtration system typically uses several filtration stages rather than relying on the RO membrane alone. Pre-filters can remove sediment and reduce chlorine before water reaches the membrane, helping protect it and improve its performance. Additional post-filtration can further improve taste and odor.

A typical multi-stage RO process can include:

Sediment filtration: Captures particles such as dirt, rust, and sediment.
Carbon filtration: Helps reduce chlorine, certain chemicals, and compounds that affect taste and odor.
RO membrane: Reduces many dissolved contaminants, including certain metals, salts, fluoride, and other impurities.
Remineralization: Adds selected minerals back into the treated water to improve taste.
Post-carbon filtration: Provides final polishing before the water reaches the drinking faucet.

For Los Angeles homeowners, this distinction matters. A Reverse Osmosis System installed at a dedicated drinking water point can provide targeted treatment for water used for drinking, cooking, and other food-related purposes while leaving the rest of the home's water supply unchanged. This makes reverse osmosis particularly useful when the primary concern is the quality and taste of water coming directly from the kitchen faucet.

Before choosing a system, homeowners should consider their local water report, any concerns identified through water testing, and the contaminants they specifically want to reduce. A filtration professional can then help determine which combination of technologies is appropriate for the home.

9 Contaminants a Reverse Osmosis System Can Remove

The exact contaminants a system can reduce depend on its membrane, filtration stages, specifications, and certifications. That's why homeowners should look beyond a general "RO removes contaminants" claim and review the performance information for the specific system they're considering. These are the general contaminants your reverse osmosis system can remove.

1. Lead

Lead is one of the drinking water contaminants that deserves particular attention because it can enter water through plumbing materials, service lines, faucets, and fixtures. It isn't typically present because of the water source itself. Instead, it can be introduced as water moves through older plumbing components.

The challenge is that lead contamination isn't something you can identify by looking at a glass of water. Water can appear completely clear while still containing trace amounts of lead. This makes filtration and regular water testing important considerations for homeowners concerned about their household water quality.

A Reverse Osmosis System can help reduce lead from drinking water when the system is appropriately certified and maintained for that purpose. The RO membrane acts as a barrier that can reject many dissolved substances, including lead.

For Los Angeles homeowners, an RO system can provide an additional point-of-use treatment option for water used directly for:

Drinking
Cooking
Making coffee and tea
Preparing baby formula
Filling reusable water bottles

Homeowners should always check the specific contaminant-reduction claims and certifications for an RO system rather than assuming every model provides the same level of lead reduction.

2. Arsenic

Arsenic can occur naturally in groundwater and can also enter water supplies through certain industrial and agricultural activities. It has no distinctive taste, smell, or color, so its presence can't be determined through everyday observation.

This is particularly relevant for Los Angeles homeowners because arsenic has been detected in the city's drinking water. As noted earlier, LADWP's 2025 water quality report recorded a maximum arsenic level of 7.0 µg/L. The reported concentration was within the applicable regulatory standard, but it illustrates why homeowners may still want to understand the specific substances present in their water.

Reverse osmosis is commonly used as a treatment method for reducing arsenic in drinking water. The effectiveness depends on the type of arsenic present, the system's membrane and configuration, and the manufacturer's certified performance.

If arsenic reduction is one of your concerns, look for a Reverse Osmosis System with documented performance for arsenic rather than relying on general claims about RO filtration.

3. Fluoride

Fluoride is another dissolved substance that reverse osmosis can help reduce. Municipal water systems may add fluoride to drinking water as part of community fluoridation programs, and naturally occurring fluoride can also be present depending on the water source.

Unlike sediment or visible particles, fluoride remains dissolved in water, which means conventional sediment filters cannot effectively address it. Reverse osmosis membranes can reduce fluoride because of their ability to reject many dissolved ions and compounds.

For homeowners who specifically want to reduce fluoride in their drinking water, an RO system can provide targeted treatment at the kitchen faucet.

This can be useful for water used for:

Drinking
Cooking
Preparing beverages
Making ice
Filling water bottles

The level of fluoride reduction varies by system, so homeowners should review the manufacturer's specifications and certification information before choosing a filtration system.

4. PFAS and Other "Forever Chemicals"

PFAS, or per- and polyfluoroalkyl substances, are a large group of manufactured chemicals used in products and industrial applications because they resist heat, oil, stains, and water. Their persistence in the environment has made them an increasing concern for water quality professionals and homeowners.

PFAS can be particularly challenging because they are present at very low concentrations and cannot be detected through taste, smell, or appearance. Different PFAS compounds can also behave differently during treatment, so filtration performance depends on the specific system and compounds being addressed.

Reverse osmosis can help reduce certain PFAS from drinking water when the system has been tested and certified for those contaminants. Homeowners concerned about PFAS should therefore look for specific performance data rather than assuming that any RO system will provide the same level of reduction.

For Los Angeles homeowners researching drinking water contaminants, checking local water quality information alongside the specifications of a filtration system can provide a clearer picture of what treatment may be appropriate.

5. Chlorine

Chlorine serves an important purpose in municipal water treatment: It helps control harmful microorganisms as water travels through distribution systems. However, some homeowners dislike the taste or smell of chlorine in their tap water.

Unlike lead, arsenic, or fluoride, chlorine is primarily addressed through activated carbon filtration rather than the RO membrane itself. That's why a well-designed reverse osmosis system typically includes carbon filtration before the water reaches the membrane.

Carbon filtration can help reduce chlorine and compounds that contribute to unpleasant taste and odor. This can make tap water more appealing for drinking and cooking while allowing homeowners to maintain an in-home filtration system rather than relying on bottled water.

For homeowners comparing a Reverse Osmosis System for their Los Angeles home, looking at the complete filtration process is important. The membrane gets much of the attention, but the pre- and post-filtration stages also contribute to the quality and taste of the finished drinking water.

6. Heavy Metals

Heavy metals can enter drinking water through natural sources, industrial activity, or plumbing materials. Lead is one example, but other metals may also affect water quality depending on the source and local infrastructure.

The challenge with many heavy metals is that they can be present at levels that aren't obvious from the water's appearance or taste. A glass of water can look perfectly clear while containing dissolved substances that require specialized treatment to reduce.

Reverse osmosis can help reduce certain heavy metals because its semipermeable membrane is capable of rejecting many dissolved ions. The actual reduction rate depends on the specific metal, water chemistry, membrane, and overall system configuration.

Homeowners should review the contaminant-specific performance information for any system they're considering rather than assuming that every Reverse Osmosis System performs identically.

7. Total Dissolved Solids

Total dissolved solids, commonly called TDS, refers to the combined amount of dissolved substances present in water. These can include minerals, salts, metals, and other dissolved materials.

TDS itself doesn't identify which substances are in the water, so a high TDS reading doesn't automatically mean that water is unsafe to drink. However, elevated dissolved solids can affect taste and may indicate that additional water treatment is worth investigating.

Reverse osmosis membranes are highly effective at reducing many dissolved solids. LA Water Solutions states that its RO drinking water system can reduce total dissolved solids as part of its multi-stage filtration process.

For homeowners seeking purified drinking water, TDS reduction can be one of the practical advantages of reverse osmosis. The process can significantly reduce many dissolved substances, while additional filtration stages help improve the taste of the treated water.

8. Bacteria and Microbial Impurities

Bacteria and other microorganisms are different from dissolved minerals and chemicals. Their presence and treatment requirements depend heavily on the water source and the condition of the plumbing system.

An RO membrane can act as a physical barrier against many microorganisms because of its extremely small filtration capability. However, homeowners should not assume that an RO system alone is appropriate for every microbial contamination concern.

If bacterial contamination is suspected, professional water testing should come first. The results can determine what type of treatment is appropriate and whether additional disinfection technology is needed.

This distinction is important when choosing a home water purification system. A filtration system should be selected according to the actual characteristics of the water rather than based on a general assumption that one technology addresses every possible contaminant.

9. Certain Chemicals and Other Dissolved Impurities

Drinking water can contain a variety of chemical compounds and dissolved substances depending on its source, treatment, and surrounding environment. Some may affect taste or odor, while others may require more specialized treatment.

A multi-stage RO system can address different types of impurities through different filtration technologies. Activated carbon, for example, can help reduce chlorine and certain chemicals, while the RO membrane handles many dissolved contaminants.

This combination is one reason homeowners researching a Reverse Osmosis System should look at the complete system rather than focusing exclusively on the membrane. The pre-filters, RO membrane, post-filter, and any remineralization stage all have specific purposes.

Why a Reverse Osmosis System Is Different From a Basic Water Filter

A basic carbon filter and an RO system don't provide the same type or breadth of filtration.

Carbon filters are commonly used to improve taste and odor and reduce chlorine and certain organic compounds. They're useful for specific water quality concerns, but they aren't intended to remove every type of dissolved contaminant.

Reverse osmosis adds a semipermeable membrane to the filtration process. This allows the system to target many dissolved substances that conventional filtration may leave behind.

For Los Angeles homeowners comparing a water filtration system for home use, the choice ultimately depends on what you want the system to accomplish. Someone primarily concerned with chlorine taste may have different needs than a homeowner looking to reduce fluoride, arsenic, lead, PFAS, or TDS.

What to Look for in a Drinking Water System

Choosing a drinking water system requires more than comparing the number of filtration stages. Consider these factors before making a decision:

Contaminant reduction: Check which specific contaminants the system is tested or certified to reduce.
Filtration stages: Understand what each stage does and how the stages work together.
RO membrane: Review the membrane's performance and expected lifespan.
Remineralization: Some systems add selected minerals back into treated water to improve taste.
Filter replacement: Consider how frequently filters need to be replaced and how easy they are to change.
Water production: Make sure the system can produce enough treated water for your household's drinking and cooking needs.
Installation: Professional installation can help ensure proper connections, system configuration, and leak protection.
Water testing: If you're concerned about a particular contaminant, testing can help determine which treatment approach makes sense for your home.

A system should ultimately match your home's water quality and your family's needs rather than simply offering the longest list of features.

Get Cleaner, Better-Tasting Drinking Water at Home

The quality of the water you drink and use for cooking deserves more attention than taste and appearance alone. For Los Angeles homeowners concerned about contaminants such as lead, arsenic, fluoride, PFAS, chlorine, and dissolved solids, point-of-use reverse osmosis can provide an additional level of filtration tailored to drinking water.

LA Water Solutions' Alpha RO Drinking Water System combines multiple filtration stages to reduce a broad range of contaminants. The system uses sediment and carbon filtration, an RO membrane, alkaline remineralization, and post-carbon filtration to produce treated water through a dedicated drinking water faucet. Its design also provides up to 100 gallons of treated water per day and includes quick-change filters for easier maintenance.

If you're looking for a Reverse Osmosis System for your Los Angeles home, LA Water Solutions can help you determine which drinking water solution fits your home's water quality and daily needs.

Frequently Asked Questions

1. What does a reverse osmosis system remove from drinking water?

A reverse osmosis system can reduce many dissolved contaminants, including certain metals, fluoride, arsenic, salts, and total dissolved solids. The exact contaminants and reduction rates vary by system, so homeowners should review the manufacturer's

specifications and certifications.

2. Does reverse osmosis remove lead?

Yes. Reverse osmosis can reduce lead from drinking water when the system is appropriately designed and certified for lead reduction. Check the specific system's performance data before installation.

3. Can reverse osmosis remove PFAS?

Reverse osmosis can reduce certain PFAS compounds. Because PFAS includes many different chemicals, homeowners should look for systems with specific testing or certification for the PFAS compounds they want to address.

4. Does reverse osmosis remove fluoride?

Yes. RO membranes can reduce fluoride because they can reject many dissolved ions. The actual reduction rate depends on the membrane and system configuration.

5. Does reverse osmosis remove arsenic?

Reverse osmosis can reduce certain forms of arsenic. Performance depends on the type of arsenic present, water chemistry, and the specific RO system.

6. Does reverse osmosis remove chlorine?

Chlorine is primarily reduced through the activated carbon stages commonly included in multi-stage RO systems. The carbon filtration also helps improve the taste and odor of treated water.

7. Does reverse osmosis remove bacteria from drinking water?

An RO membrane can provide a physical barrier against many microorganisms, but treatment requirements vary depending on the water source and contamination. If bacterial contamination is suspected, professional water testing should determine the appropriate treatment.

8. Does reverse osmosis remove minerals from water?

RO can reduce many dissolved minerals and salts. Some systems include a remineralization stage that adds selected minerals back into the treated water to improve taste.

9. Is reverse osmosis water safe to drink?

When properly installed and maintained, a reverse osmosis system can provide treated drinking water. Homeowners should select a system appropriate for their water quality and follow the manufacturer's maintenance and filter replacement recommendations.

10. How often do reverse osmosis filters need to be replaced?

Replacement schedules vary by filter type, system design, water quality, and household usage. Following the manufacturer's recommended replacement schedule helps maintain filtration performance and water quality.