How can you reduce PFAS in water? The quick answer

To reduce PFAS in tap water, the most suitable technologies are those with documented performance for the substances in question. Reverse osmosis can reduce the concentration of certain PFAS through its membrane, while some activated carbon systems can also capture some of these substances. However, the actual level of reduction varies depending on the type of PFAS, the filter, its capacity, the flow rate, water quality, and maintenance frequency.

What are PFAS?

PFAS, or per- and polyfluoroalkyl substances, are a family of chemicals used in many industrial applications and consumer products.

They are studied extensively because of their high persistence in the environment. Some can be found in soil, groundwater, or water intended for drinking.

For general information about these substances, also see: the ANSES page on PFAS .

Can PFAS present in water be filtered out?

Yes, certain water treatment technologies can reduce the concentration of certain PFAS. However, it is important not to treat PFAS as a single substance.

This family includes many compounds with different characteristics. A technology can therefore perform very well for some molecules and less well for others.

The level of reduction depends in particular on:

• the type of PFAS present;
• its initial concentration;
• the technology used;
• the quality of the filter media or membrane;
• the water flow rate;
• how long the filter has been in use;
• system maintenance.

For this reason, it is better to rely on the documented performance of the specific system than on a general claim applied to all devices.

How does reverse osmosis work on PFAS?

Reverse osmosis is a water treatment technology that uses a semipermeable membrane. Water is pressurized so that some of it passes through this membrane, while another portion carries away some of the retained substances.

This process can reduce the concentration of many dissolved substances, including certain PFAS.

However, actual performance depends on:

• the membrane installed;
• the operating pressure;
• the composition of the water;
• the type of PFAS;
• pretreatment;
• system maintenance.

An RO system should therefore not be presented as guaranteeing exactly the same reduction rate in every installation.

To understand this technology in more detail: see our guide to reverse osmosis .

The different stages of an RO system

A home RO system generally consists of several complementary stages.

1. Sediment pre-filtration

An initial filter can capture certain particles such as sand, deposits, or rust.

This stage mainly serves to protect components downstream in the system.

See: our pre-filtration solutions .

2. Activated carbon filtration

An activated carbon filter is often used before the membrane. Depending on the media used, it can reduce certain organic substances and chlorine, among other things.

This stage can also help protect the reverse osmosis membrane.

3. Reverse osmosis membrane

The membrane is the central component of the RO system. Some of the water passes through this membrane, while the other stream carries some of the retained substances to the drain.

This is a key stage where the concentration of many dissolved compounds can be substantially reduced.

See: membranes for RO systems .

4. Post-filtration

Some systems then use a post-filter, such as an activated carbon filter, to improve certain water characteristics before dispensing.

5. Tank or direct flow

Depending on the model, RO water can then be stored in a tank or produced directly on demand.

These two configurations alone do not determine effectiveness against PFAS: the membrane, the complete system, and its operating conditions are the main factors to consider.

To compare these two technologies: direct-flow or tank-based RO system?

PFAS: reverse osmosis or activated carbon?

Reverse osmosis and activated carbon are two technologies that can help reduce certain PFAS, but they work very differently.

This table outlines the differences in how these technologies work. It does not guarantee performance for a specific contaminant. The performance of the product used must be verified separately.

Be cautious about advertised removal percentages

A rate such as “95 %,” “99 %,” or “complete removal” should not automatically be applied to all PFAS and all RO systems. For a figure to be meaningful, you need to know the compound tested, its initial concentration, the testing protocol, the membrane used, and the operating conditions.

What limitations should you know about?

Even when a technology can reduce certain PFAS, several limitations must be taken into account.

• There are many PFAS: they do not all behave the same way.
• Performance declines if the system is poorly maintained: a saturated filter or degraded membrane may perform less effectively.
• Reverse osmosis produces wastewater: the volume depends heavily on the device, pressure, and operating conditions.
• Incoming water quality matters: water composition can affect the system’s overall operation.
• No home system should be considered universal: you need to choose the technology based on the problem actually identified.

How do you choose a system to reduce PFAS?

Before buying a system solely on the basis of an “anti-PFAS” claim, you should check several criteria.

To compare purchasing criteria: see our guide to choosing a home RO system .

Why is maintenance essential?

A filtration technology is only truly effective if it is maintained properly.

In an RO system, you should monitor in particular:

• the condition of the pre-filters;
• how long the activated carbon has been in use;
• membrane performance;
• the production flow rate;
• the overall quality of the water produced;
• the manufacturer’s recommendations.

Replacement frequency should not be based solely on a generic time interval: it depends on the model, incoming water, and the volume actually treated.

See our guide: how to maintain an RO system .

Considering an RO system?

First compare the flow rate, wastewater, membrane type, maintenance, and specifications that match your installation.

Frequently asked questions about PFAS and water filtration

Can an RO system reduce PFAS?

Yes, reverse osmosis can reduce the concentration of certain PFAS. However, actual performance depends on the compound in question, the membrane, the system, and its operating conditions.

Does an RO system remove 100 % of PFAS?

It is better not to present an RO system as consistently removing 100 % of PFAS. This family includes many compounds, and performance must be verified for the specific system and substances.

Does activated carbon filter out PFAS?

Some activated carbon systems can reduce some of the PFAS present in water. Their effectiveness depends in particular on the type of carbon, the compound in question, the flow rate, and filter saturation.

Reverse osmosis or activated carbon: which should you choose?

It depends on your goal. Reverse osmosis also substantially reduces many dissolved salts, while activated carbon works primarily through adsorption. A system can also combine both technologies.

Why does an RO system often use a carbon filter?

Activated carbon can serve as pretreatment before the membrane. It complements the system and can help protect the membrane against certain substances.

How often should you change the filters?

The frequency depends on the filter, incoming water quality, the volume treated, and the manufacturer’s recommendations. Avoid applying the same time interval to every device.

How do you know if your water contains PFAS?

The presence of PFAS cannot be determined by the taste, smell, or appearance of water. It requires appropriate analytical data. Information from the relevant authorities and laboratory analyses are the preferred sources.

Sources and references

Information about PFAS must be supported by institutional or scientific sources, particularly when it concerns their effects or the performance of a treatment technology.

• ANSES – PFAS: persistent chemicals

For any numerical reduction value added to this article later, directly citing the corresponding study, certification, or test is recommended.

About this guide

This content is written by the Josmose team based on our experience with water treatment solutions and the sources cited.

Josmose sells RO systems, membranes, filters, and consumables accessible from this page.