Many substances harmful to human health are finding their way into our drinking water.

These include the so-called 'forever chemicals,' per- and polyfluoroalkyl substances (PFAS). A group of fluorinated chemical compounds, they are resistant to degradation, bioaccumulate in tissues, and are highly mobile in the environment.

Widely used as non-stick coatings, stain repellents and surfactants, among other industrial applications, PFAS have become a major environmental and health concern over the last 10 to 20 years.

PFAS can now be detected almost anywhere using the right analytical equipment. This has raised concerns about the health effects of current exposure levels.

Multiple exposures

Our exposure to PFAS comes from drinking water, air, food and, to a lesser extent, absorption through skin. Although it is difficult to reduce exposure by the airborne route, more frequent cleaning of the house can help to minimize the inhalation of dust containing PFAS. However, this route of exposure requires further research.

Significant levels of PFAS can also be found in food and food packaging. As long as regulation in this area remains limited, it will be particularly difficult to try to reduce our exposure to PFAS by changing our eating habits, unless it becomes clear what food is less contaminated or if a large portion of the products available in the grocery shop are contaminated.

Drinking water remains the easiest source of PFAS to treat when we seek to reduce our overall exposure to these substances. Termeh Teymoorian, a doctoral student in chemistry at the Université de Montréal, is working on PFAS in water. She is co-supervised in her doctoral thesis by Sébastien Sauvé, a professor in environmental chemistry at the Université de Montréal and a specialist in emerging contaminants, and Benoit Barbeau, a professor at Polytechnique Montréal and co-holder of the Industrial Chair in Drinking Water.

We recently published an article in Frontiers in Environmental Chemistry in which we evaluate the effectiveness of domestic water filters in eliminating PFAS.

Drinking water treatment

The most effective way to treat drinking water is to modernize treatment plants to eliminate PFAS, thereby guaranteeing safe drinking water for everyone, whatever their socio-economic status.

This modernization effort is all the more essential given that conventional water treatment is often ineffective in eliminating these substances. However, specific treatments for PFAS can be costly and time consuming to implement.

Consuming bottled water, while an easy solution, is not necessarily affordable for everyone. When compared to tap water, botteled water also has a significant ecological footprint, particularly due to the transport and disposal of containers.

Boiling water is not an effective way to destroy PFAS. In some situations, bringing water to a boil does reduce PFAS concentrations in the water very slightly, but it transfers some of their volatile components into the air, so the problem is displaced rather than solved.

Residential treatment options

For domestic water treatment, installing a filter at the main kitchen sink (point-of-use or POU treatment) is the most cost-effective option. Treating all the water in the house is unnecessary and more expensive. Baths and showers are not significant sources of PFAS exposure.

Residential treatment options include:

1. Nanofiltration and reverse osmosis systems

These systems, if certified to eliminate PFAS, are considered effective. However, their effectiveness depends on the quality of the water and the contaminants present. Under-sink systems are more expensive at the time of initial purchase and require periodic replacement of the cartridge or membrane, usually once a year. A plumber may be necessary to install it, and it requires space under the sink.

2. Pitcher-type filters

These methods are simple, relatively cheap and quick to set up. However, conventional pitchers are often ineffective at removing PFAS, especially the newer, shorter-chain compounds. Effectiveness varies according to the characteristics of the water and the types of contaminants.

Pitcher filtration performance

We tested the performance of different brands of pitcher filters in an independent evaluation of their ability to remove PFAS using tap water from two Canadian municipalities.

The full results are available online in our study, but are summarized below:

Zerowater pitchers: Certified by the National Sanitation Foundation (NSF) to remove PFAS, our tests showed over 96 per cent removal after 160 L of filtration for both types of water tested.

Clearly Filtered pitchers: Certified by the Water Quality Association (WQA) for the elimination of PFAS, with an elimination rate of over 96 per cent after 160 L of filtration in our tests.

Aquagear pitchers: Although deemed effective according to a test carried out by an independent laboratory, our tests showed a lower elimination rate of 60-77 per cent.

Brita Elite filter jugs: These jugs are neither designed nor certified to eliminate PFAS. The tests carried out show elimination of only 20-48 per cent, and partial tests have shown inferior performance for the conventional Brita filter.

The choice of residential treatment to remove PFAS from tap water depends on the user's preferences. Pitcher filters are simple, but their long-term cost can be higher than that of adsorption or reverse osmosis filters installed under the sink. To eliminate PFAS correctly, it is important to choose certified products for their elimination.