Water pollutants 2/2: Which Water Should You Drink and How Should You Filter It?

📌 This article is Part 2 of our two-part series on water pollutants. Part 1 is available here: Water pollutants 1/2: What Can Actually Be Found in Our Water →

In Part 1, we saw that drinking water can contain traces of PFAS, pesticides, nitrates, lead, disinfection by-products, as well as micro- and nanoplastics, and we looked at what is currently known about their effects on health.

Now comes the most important question: what do we actually do with this information?

Should you stop drinking tap water? Switch to bottled water? Buy a filter jug? Install a reverse osmosis system? Test your water before choosing?

There is no universal answer, because not all water has the same composition and not all filtration systems remove the same substances.

The goal is to understand what may potentially be in your water and which solution actually fits your situation.

First step: look at what is in your water

Before buying a filter, look at the results for your local area.

In France, data from health monitoring carried out by the Regional Health Agencies are public and available municipality by municipality on the Ministry of Health website.

Monitoring does not stop at the outlet of the treatment plant: samples are taken from the water source, at the point of distribution, throughout the network and at consumers' taps.

You can look in particular at:

pesticides and their metabolites;
nitrates;
PFAS when available;
lead;
microbiological parameters;
disinfection by-products;
water hardness and mineral content.

The annual summary of your water quality is also available through your water quality information notice included with your bill.

This is the first level of information and, for many people, it is already extremely useful.

But your tap may tell a slightly different story

Municipal data tell us about the water being distributed.

They do not always allow us to know exactly what happens in the final few metres between the public network and your glass.

The clearest example is lead.

Lead is generally absent from the water at the source and when it leaves treatment facilities. However, it can be released from certain old pipes, connections or plumbing components.

Testing the water directly at your tap may therefore be relevant in certain situations:

an older home or suspected old plumbing;
a known local issue involving a particular contaminant;
proximity to a particularly exposed industrial or agricultural area;
use of a private well or private water source.

In that case, it is better to use an approved or accredited laboratory, which can specifically test for the contaminants concerned and provide reliable, interpretable concentrations, rather than a simple general indicator of water quality.

Which filtration system should you choose?

This is the question that should come before any purchase: what am I actually trying to remove from my water?

Not all so-called "filtration" solutions belong in the same category. A filter jug can perfectly well improve the taste of water and reduce certain contaminants, but it does not have the same capacity or performance as an under-sink system or reverse osmosis.

Three main options are particularly relevant:

| System | What it can reduce | Advantages | Limitations / points to watch | Cost | | --- | --- | --- | --- | --- | | Filter jug (e.g. Brita: activated carbon + often ion-exchange resin) | Chlorine, tastes and odours; depending on the cartridge: certain pesticides, metals and some PFAS | Simple, no installation required, inexpensive, retains most of the minerals in the water | Performance varies greatly depending on the cartridge; limited capacity; frequent replacement required. This is not broad-spectrum filtration. Moist activated carbon may also encourage bacterial colonisation as the cartridge ages, when water stagnates or when maintenance is inadequate. | € | | Under-sink activated carbon / carbon block filter, sometimes combined with ion-exchange resin | Chlorine, many organic compounds; depending on the system: lead, pesticides and several PFAS | More filtration media and generally greater contact time than a jug; good flow rate; no wastewater; retains minerals | Does not effectively remove all dissolved contaminants: nitrates, salts and some short-chain PFAS may pass through. Cartridges need regular replacement. Carbon can harbour biofilm when water stagnates or maintenance is poor. | €€ | | Reverse osmosis, generally combined with activated-carbon and sediment prefilters | Very broad filtration: PFAS, nitrates, lead and many other metals, dissolved salts, pesticides and particles, depending on the system | One of the most comprehensive domestic solutions; particularly useful when trying to reduce several families of contaminants at once | More expensive and bulkier; greater installation and maintenance requirements; also removes a large proportion of minerals (some systems include a remineralisation stage); produces wastewater. Tanks and tubing can also develop biofilms if poorly maintained. | €€€ |

What about ultrafiltration or nanofiltration?

Other membrane technologies are also increasingly being offered in domestic systems.

Ultrafiltration mainly retains particles, bacteria and certain microorganisms through a very fine membrane, while allowing most dissolved minerals to pass through. However, it is much less suited to dissolved chemical contaminants such as nitrates, salts or many PFAS.

Nanofiltration goes further: its tighter membrane can reduce certain salts, metals and organic contaminants and has shown effectiveness against many PFAS, including some short-chain PFAS. However, it generally remains less "broad-spectrum" than reverse osmosis, and its performance depends heavily on the membrane used.

In practice, these can therefore be interesting alternatives in certain domestic systems, but once again you need to look at the performance actually tested for the contaminants you want to remove.

Look at independent testing, not just the technology

A manufacturer may claim that a system "filters PFAS" without this meaning that it has been robustly tested across all the contaminants you are concerned about.

Before buying, look primarily at whether performance has been measured by an independent laboratory, on the exact model you are considering, and whether the results are clearly reported: which substances were tested, at what concentrations and what percentage was actually removed?

This is particularly important for PFAS: a filter may perform well for PFOA or PFOS but much less effectively for other PFAS, particularly certain short-chain compounds.

Look for complete independent test results for the exact filter and pollutants you want to reduce.

Maintenance is part of filtration

A filter is only effective as long as it is properly maintained.

Activated carbon works in part through adsorption: contaminants bind to its surface. Its capacity is therefore finite. Once the cartridge reaches the end of its useful life, its performance declines.

You therefore need to follow:

the recommended cartridge replacement schedule;
the maximum volume of water specified by the manufacturer;
regular cleaning of the jug, tank and tubing;
recommendations for periods of prolonged non-use.

There is also a microbiological consideration. A wet filter in which water stagnates can become an environment that favours bacterial biofilm development, particularly when the system is poorly maintained or used beyond its recommended lifespan.

This applies to jugs and activated-carbon filters, but not only to them: the tanks and tubing of reverse osmosis systems also need proper maintenance.

In other words, an excellent system that is poorly maintained can lose much of its value.

So, is reverse osmosis the best solution?

It is one of the domestic technologies offering the broadest spectrum of filtration.

Water is pushed under pressure through an extremely fine membrane that retains a large proportion of dissolved substances. Domestic systems generally combine this membrane with several prefilters, including activated carbon.

They can therefore substantially reduce many PFAS, nitrates, lead and other metals, various dissolved salts, as well as many organic contaminants, depending on the system used. The EPA identifies reverse osmosis as one of the domestic technologies capable of substantially reducing PFAS.

It is therefore particularly interesting when:

several different contaminants are present or are a concern;
PFAS are a priority;
you want broad filtration rather than targeted treatment;
the quality of your local water justifies this level of filtration.

But "more filtration" does not automatically mean "better for everyone".

Reverse osmosis has several limitations:

it costs more to purchase and maintain;
prefilters need to be replaced and the membrane needs periodic replacement;
it also removes a large proportion of the calcium and magnesium naturally present in water;
it produces a certain amount of wastewater;
and tanks and tubing need to be maintained to limit biofilm development.

Environmental performance also varies significantly between systems.

If your water is compliant and your main goal is to reduce chlorine, improve taste or lower certain targeted contaminants, a good certified activated-carbon filter may be more than sufficient.

However, when the goal is to reduce several families of contaminants, particularly PFAS, reverse osmosis is currently one of the most comprehensive domestic options available.

Should water be remineralised after reverse osmosis?

This is an area where there are many contradictory claims. Reverse osmosis substantially reduces the calcium and magnesium naturally present in water.

These minerals can contribute to our nutritional intake, sometimes to a meaningful degree when the water is particularly mineral-rich.

However, the WHO does not currently define a minimum concentration of calcium, magnesium or hardness required for health in drinking water, because the available evidence is insufficient to establish a universal value. Food obviously remains a major source of these minerals.

Remineralisation after reverse osmosis may nevertheless have several benefits: improving taste, reintroducing calcium and magnesium, and modifying the physicochemical characteristics of highly demineralised water.

If reverse-osmosis water is going to be your main source of drinking water over the long term, choosing a system that remineralises the water appropriately is a reasonable option, particularly if you want a profile closer to naturally mineralised water.

What about boiling your water?

Boiling water is highly effective at reducing a microbiological risk when public-health guidance recommends doing so.

But it is not a method for filtering chemical pollutants.

Boiling your water therefore does not replace filtration when the goal is to reduce micropollutants.

Tap water or bottled water?

Bottled water is also subject to health monitoring. But bottled does not mean contaminant-free. The source itself may be exposed to pesticides or PFAS, and plastic packaging adds the issue of micro- and nanoplastics.

Tap water has one important advantage: its local quality can be checked and it can be filtered specifically.

For a large proportion of the population, compliant, filtered tap water can therefore be a good option.

In practice: what to look at before choosing

What do my local water analyses show? Start with the data already available.
Does my home have a particular risk factor? For example, an old internal plumbing network or pipes that may contain lead.
Which contaminant am I trying to reduce? Chlorine? PFAS? Pesticides? Lead? Nitrates?
Does the manufacturer provide independent evidence that the system reduces this contaminant? Look at the results, testing conditions and an independent certification that corresponds to the specific contaminant.
Am I prepared to maintain the system properly? An excellent filter that is poorly maintained becomes a poor filter. Cartridge replacement frequency, cleaning and maintenance are integral to its performance.

And what about measuring your own exposure?

Water testing tells you about one potential source of exposure. But it does not tell you what has actually been absorbed by your body, nor where your overall exposure comes from.

At Lucis, our Environmental Toxicology Analysis measures three toxic metals in the blood: lead, mercury and cadmium.

The aim is to identify unusually high exposure and then put it into context: water and housing for lead, but also diet, smoking, environment or occupational exposure depending on the metal concerned.

Measuring is only the starting point. The value lies in knowing what to do with the data, and Lucis guides you from measurement all the way through to concrete actions.

Listen to the episode

In our latest Lucis Podcast episode, we explored all of these questions with Alexandre, founder of Sküma Water, and Dr Christian Boyer, PhD in Health Biology.

Alexandre explains the different filtration technologies, their limitations and why Sküma chose reverse osmosis combined with water remineralisation.

If you are considering investing in a filtration system, the episode is especially useful for understanding what you are buying and why, rather than choosing based solely on a promise of "purity".

Scientific references

ANSES. Opinion on PFAS in water intended for human consumption: effectiveness of drinking-water treatment processes. 2026.
ANSES. Materials and objects in contact with water, and products and processes used to treat public drinking water.
Environmental Protection Agency (EPA). Identifying Drinking Water Filters Certified to Reduce PFAS.
Environmental Protection Agency (EPA). Reducing PFAS in Your Drinking Water with a Home Filter.
Herkert NJ, Merrill J, Peters C, et al. Assessing the Effectiveness of Point-of-Use Residential Drinking Water Filters for Perfluoroalkyl Substances (PFASs). Environmental Science & Technology Letters. 2020;7(3):178-184. doi:10.1021/acs.estlett.0c00004
French Ministry of Health. Approved laboratories for health monitoring of water. 2026.
French Ministry of Health. Monitoring the quality of tap water. 2026.
Mulhern R, et al. Are carbon water filters safe for private wells? Evaluating the occurrence of microbial indicator organisms in private well water treated by point-of-use activated carbon block filters. International Journal of Hygiene and Environmental Health. 2021;238:113852. doi:10.1016/j.ijheh.2021.113852
Payment P. Bacterial colonization of domestic reverse-osmosis water filtration units. Canadian Journal of Microbiology. 1989;35(11):1065-1067. doi:10.1139/m89-178
Qian N, Gao X, Lang X, et al. Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. Proceedings of the National Academy of Sciences. 2024;121(3):e2300582121. doi:10.1073/pnas.2300582121
Tobin RS, Smith DK, Lindsay JA. Effects of activated carbon and bacteriostatic filters on microbiological quality of drinking water. Applied and Environmental Microbiology. 1981;41(3):646-651. doi:10.1128/AEM.41.3.646-651.1981
World Health Organization (WHO). Chemical fact sheets: Hardness. 2022.
World Health Organization (WHO). Guidelines for Drinking-water Quality. Fourth edition incorporating the first and second addenda. 2022.

The information shared in this article is provided for educational purposes only. It is not a substitute for medical advice, diagnosis or care from a qualified healthcare professional.