What do Water Filters Remove?

Wondering whether a water filter will effectively remove the contaminants detected in your water?

We’ve been testing and reviewing water filters for WaterFilterGuru for over a decade, and in that time, we’ve gained a comprehensive understanding of which contaminants are typically removed by which systems.

Here, we’ve listed the most common water filters and the contaminants they remove, based on our own experience and scientific evidence available online.

The 5 most common water filter media we’ll be discussing are:

• Mechanical filters
• Adsorption filters
• Ion exchange filters
• Membrane filters
• Distillation

🚰 What do Mechanical Filters Remove?

Mechanical filters remove sediment, dirt, sand, and other particulates in water using physical filtration.

We use mechanical filters to protect whole-home systems from sediment, either as standalone point-of-entry filters or as pre-filters included with multi-stage systems.

These filters are particularly important for well water, which is groundwater (as opposed to most city water supplies, which are surface water), and has a natural sediment content.

We’ve also used mechanical filters downstream of city water POE tank-based systems. In this case, the mechanical filter prevents media from the tank-based system from entering our home’s plumbing system.

There’s a lot of scientific evidence that supports the use of mechanical filters for sediment removal. They’re highlighted in this UGA Extension report, which says they can remove “larger suspended material” from water, including silt, sand, loose scale, clay, and organic matter.

Mechanical filters have been used for decades to address sediment and other suspended particulates in water – the value of these filters in the water purification process was even discussed in the Journal of the Royal Sanitary Institute back in 1915.

📥 What do Adsorption Filters Remove?

Adsorption filters, including catalytic carbon filters, granular activated carbon filters, and carbon block filters, remove chemicals like chlorine, taste, and odors, pesticides, PFOA and PFOS, disinfection byproducts, some volatile organic compounds, a few metals, and gasoline.

Adsorption filtration media is the most commonly used media used in most of the filters we’ve tested so far.

One of the best examples of an adsorption filter is the Brita Elite gravity water filter pitcher, which uses an activated carbon filter that’s certified by IAMPO and the WQA to reduce chlorine, Particulates Class I, lead, mercury, cadmium, asbestos, benzene, PFOA, PFOS, BPA, estrone, ibuprofen, naproxen, microplastics, nonyl phenol.

In our testing, this pitcher reduced 100% barium and 97% copper in our water, as well as 100% chlorine and its associated tastes and odors.

Other activated carbon water filters we’ve tested include the Clearly Filtered pitcher, the Epic Pure filter, and the PUR Plus filter. In our testing, these reduced 100% chlorine and addressed other contaminants in our water more comprehensively. They combine activated carbon with other filter media, like ion exchange resin and KDF media, which can more effectively address the contaminants detected in our water (like uranium, fluoride, nitrate, etc.).

The adsorption filtration method has been widely studied and is considered a safe, effective water treatment solution, particularly for addressing chlorine, tastes, and odors.

The EPA notes that granular activated carbon treatment can be used to reduce solvents, industrial chemicals, fuel oil, radon and other radioactive materials, and some types of metals from water.

This evaluation of GAC for drinking water treatment, published in Drinking Water and Health, noted that properly operated granular activated carbon systems could effectively reduce a number of organic compounds, including synthetic organic chemicals.

Catalytic carbon media is another type of adsorption filter that’s formed by modifying the surface of an activated carbon filter, increasing its adsorption capabilities. This filter media can also adsorb chloramine (another type of disinfectant commonly used for treating city water) and hydrogen sulfide (which gives water a rotten egg odor).

We’ve tested several POE catalytic carbon systems, including the SpringWell CF, a tank-based system that combines catalytic carbon with KDF media, which reduced many unwanted contaminants in our water, including nickel and cobalt, copper, zinc, and barium.

🔀 What do Ion Exchange Filters Remove?

Ion exchange filters address contaminants with charged ions in water. There are two types of ion exchange filters, and the type of filter depends on the contaminants removed:

• Anion exchange removes anions, or positively charged ions, including chlorides, nitrates, arsenic, sulfate, fluoride, and nitrate.
• Cation exchange removes cations, or negatively charged ions, including calcium and magnesium ions, as well as low levels of iron and other metals, like lead, chromium, and copper.

We’ve tested numerous ion exchange systems, and we’ve found that cation exchange water treatment is most commonly used in water softeners to exchange calcium and magnesium hardness minerals with a non-scale-forming cation, like sodium or potassium. One of the best water softeners we’ve tested is the SpringWell SS, which reduced over 97% total hardness in our water, including 97.43% calcium and 97.73% magnesium.

Cation exchange water softeners are approved by the EPA as the go-to method for removing calcium and magnesium hardness minerals from water.

Many of the water filter pitchers we’ve tested combined activated carbon media with anion exchange resins. Some, like the ZeroWater pitcher, use both anion and cation exchange to reduce a greater number of contaminants. In our testing, the ZeroWater filter did a great job of removing 100% fluoride, uranium, barium, strontium, molybdenum, nitrate, and sulfate, and 97% copper. But it also greatly reduced calcium and magnesium in our water, which has no benefit in a POU system.

Not all manufacturers disclose exactly which filter media they use. This was the case for several of the water filter pitchers we tested, but we suspected the use of ion exchange media because they reduced healthy minerals and substantially increased sodium or potassium.

There are several studies that examine the ability of ion exchange to reduce select contaminants in water, including PFAS and heavy metals (nickel, copper, lead, cadmium, zinc, mercury, chromium, and arsenic).

🔎 What do Membrane Filters Remove?

Membrane filters remove a broad spectrum of dissolved solids from water, including metals, chemicals, minerals and salts, radium, bacteria, and much more.

The most common type of membrane filter for at-home drinking water filtration is a reverse osmosis unit.

We’ve tested several countertop and under-sink reverse osmosis filtration units, and all have performed exceptionally well at reducing contaminants in our water – many completely eliminated all impurities, resulting in purified water.

The AquaTru is the top-scoring countertop reverse osmosis system we’ve tested, eliminating all 11 impurities with health effects – including nitrate, fluoride, uranium, barium, copper, and strontium – in our water. It also eliminated chlorine and greatly reduced calcium and magnesium minerals.

The Waterdrop G3 P800 is the best under-sink RO system we’ve tried so far, greatly reducing or removing chlorine, arsenic, fluoride, lead, strontium, barium, nitrate, copper, manganese, selenium, and sodium.

We noticed one key difference between the reverse osmosis systems and the other water filters we tested: the RO units were able to effectively address all impurities in our water, including metals, chemicals, and minerals, while many of the filters we tested could only reduce or remove select impurities.

That’s because reverse osmosis membranes have tiny pore sizes (around 0.0001 microns) and reject all impurities that are larger than this. They’re not limited to reducing only the contaminants that can be adsorbed, or only the contaminants with an ionic charge. RO filtration systems are the most capable filters we’ve tested.

Membrane water filtration is another technology that’s far from new – it has been used for drinking water treatment for years and is heavily research-backed. This 2022 evaluation of TDS removal techniques commented that reverse osmosis has one of the highest TDS removal efficiencies (95−99%). It also mentions ultrafiltration, another membrane filtration method, as an option for reducing larger dissolved solids (UF membranes have a pore size of 0.01-0.1 microns).

You can read our comprehensive review of the Top 6 Reverse Osmosis Systems in this post 👈

⚗️ What does Water Distillation Remove?

While not a water filtration process in the conventional sense, we still want to mention water distillation in this guide because water distillers are widely available for tap water treatment.

Water distillation purifies water, so it removes everything: metals, chemicals, hardness, microorganisms, and poor tastes and odors.

There are a few exceptions: some chemicals may be able to evaporate and condense with the water molecules, meaning they’ll be retained in the purified water. Many distillers use activated carbon filters to provide chemical filtration before the purified water leaves the spout.

I personally use a distiller to create ultra-pure water for my wife’s CPAP machine. I’ve found that the water produced by my distillation system is purer and cleaner than any other water I’ve produced, and it also has the flattest, plainest taste – I wouldn’t typically recommend it as drinking water.

The water distillation process is widely acknowledged as a method of purification. This University of Nebraska-Lincoln report notes that water distillers can remove “nearly all impurities” from water, including hardness compounds, iron, manganese, sodium, fluoride, nitrate, and other dissolved solids.

The CDC comments that water distillation is highly effective at removing microorganisms including viruses, protozoa, and bacteria, as well as arsenic, common chemical contaminants, barium, organic chemicals, chromium, and more.

📝 Factors Affecting a Filter’s Contaminant Removal Abilities

There are a few key factors that affect the contaminants that water filters can remove:

• The type of filter. As you can see by our comparison of the filter types above, different types of filters address different contaminants with different levels of effectiveness. For instance, a reverse osmosis filtration system filters water much more thoroughly than an adsorption filter.
• The filter pore size. The smaller the filter’s pores, the smaller the contaminants that can be trapped in the media.
• Tap water quality. When tap water is heavily contaminated, a water filter may offer a lower percentage removal because there is a higher concentration of impurities to begin with. You may need to replace the filter more frequently as well.
• Speed of filtration. The rate at which water flows through a filter affects its contact time, and in some water filters, this affects contaminant reduction. For instance, when water has a longer contact time with an adsorptive gravity filter, the media has the opportunity to adsorb higher concentrations of contaminants.

📑 Final Word

We hope this guide helped you to understand which types of drinking water filters reduce which contaminants.

When it comes to choosing the best method to filter water in your home, this depends on which contaminants your tap water contains, and how thoroughly you want to purify it.

For instance, if your main concern is to improve your water’s taste, and reduce a handful of chemical contaminants and metals, an adsorption filter may be perfect for you.

If you want to address metals or hardness minerals, an ion exchange filter that has been performance-tested for this purpose is your best bet.

Or, to remove as many impurities as possible, a membrane water filtration system is the superior choice.

We strongly advise testing your water if you haven’t already. Knowing which contaminants different water filters remove is a great start, but it’s not super helpful information unless you know what your water contains – and therefore what you want to remove.