How Do Water Filters Work?

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Q: I’m considering buying a water filter but I don’t understand how they work. I’ve read lots of contrasting information online and need a simple explanation. Can you help?

A: We’d be happy to! Different types of water filters work in different ways to address contaminants in water. We’ve listed the most common types of water filters and how they work in this guide.

how do water filters work

🚰 What Is a Water Filter and How Does it Work?

A water filter is a system designed to remove impurities and contaminants from water. It uses physical barriers, chemical processes, or biological mechanisms to filter water, ensuring it meets specific quality standards for consumption or other purposes.

Typically, a water filter works by trapping, adsorbing, or collecting contaminants as the water flows through the filter media. These contaminants are unable to pass through to the other side of the filter, so the water that leaves the filter is improved in quality.

Some of the tap water contaminants that may be addressed by a filtration process include:

  • Chlorine and other chemicals
  • Heavy metals
  • Silt, sand, and sediment
  • Fluoride
  • Pesticides
  • Bacteria and cysts

The exact combination of contaminants targeted depends on the water filtration system you choose. The best water filters can reduce or remove hundreds of contaminants from water.

πŸ€” What’s the Purpose of a Water Filter?

The purpose of a water filter is to make water safer to drink by reducing or removing trace contaminants that may affect the overall water quality.

Most water treatment systems intend to do the following:

  • Improve water’s safety: Systems that address any contaminants with health effects aim to make tap water safer and healthier to drink.
  • Elevate aesthetic quality: Filters that reduce unpleasant tastes, odors, and staining/discoloration help to improve water’s aesthetic quality.
  • Protect plumbing: Some systems, like water softeners and iron filters, prevent corrosion and scale damage in your home’s pipes, plumbing, and appliances.

One filtration system might have a slightly different purpose than another, depending on the contaminants it’s designed to address.

For example, reverse osmosis filters are designed to purify water by reducing as many impurities as possible, while a basic water pitcher filter may only improve water’s aesthetic quality by reducing chlorine with an activated carbon filter.

πŸ”§ Where is a Water Filter Installed?

Water filtration systems are typically installed either at a point of use (such as at your kitchen faucet) or at the point of entry (the main water pipe into your home).

  • Point-of-use water filters are designed to filter water just before, or after, it leaves your plumbing. Water filter pitchers, under-sink filtration systems, refrigerator filters, faucet filters, and countertop water filters are all POU filters that treat drinking water. Showerhead filters and bath filters are POU systems that treat shower/bath water.
  • Point-of-entry water filters treat the water supplied to your whole house. The filtration process addresses water quality issues before the water can enter your plumbing, so all the tap water in your home is treated. Whole-house water filters include tank-based and cartridge-based systems.

Related: Learn which under sink systems are worth investing in this year.

πŸ“– 5 Types of Water Filters & How They Work

Here are the 5 types of water filters and how they work:

1) Mechanical Filters

There are numerous types of mechanical filters:

  • Ceramic filters: These remove contaminants of all sizes, including pathogens, with a network of pores
  • Mesh filters: These are designed to trap suspended particles, like sand and rust, while allowing water particles to pass through.

πŸ’‘ Sediment filters are the most common example of the mechanical filtration method. These filters offer physical filtration, removing large suspended particles in water.

How Do They Work?

Mechanical filters work by using a physical barrier to block contaminants like sediment, dirt, and other suspended particles.

Most mechanical filters have a micron rating, which tells you what sized contaminants can be removed. For instance:

  • A 0.5-micron filter is capable of removing tiny contaminants, like some microorganisms.
  • A 1-micron filter is capable of reducing particles that are invisible to the naked eye.
  • A 5-micron filter reduces contaminants that you may be able to see suspended in your water, like sediment or metal shavings.
Mechanical water filter cartridges

2) Absorption Filters

Activated carbon filters and activated alumina filters use adsorption to reduce a handful of common water contaminants.

πŸ“Œ There are several types of activated carbon adsorption filters. Granular activated carbon (GAC) and carbon block filters are two of the most common filters that use carbon filtration. Carbon block filters pack their media in a solid block, allowing for more thorough contaminant removal.

Adsorption filters are cheap to manufacture and don’t add anything dangerous to water, so they’re a popular choice for a variety of filter systems.

activated carbon filter cartridges

How Do They Work?

Adsorption filters work by grabbing contaminants and holding them in their pores – a bit like a sponge – using a process called adsorption.

Adsorptive filters have a large surface area. Most adsorptive filters have a pore size of around 5-10 microns.

Only contaminants that are attracted to the adsorptive media can be removed by adsorption. For instance, carbon filters predominantly target chlorine, disinfection byproducts, pesticides, herbicides, and some VOCs, but they don’t typically reduce metal ions. Activated alumina filters are capable of adsorbing fluoride, arsenic, and some selenium.

Carbon block versus activated carbon filtration

3) Ion Exchange Filters

Ion exchange filters are also commonly used in systems designed to treat tap water.

The most common use of ion exchange in water treatment takes place in a water softener, which exchanges magnesium and calcium ions with sodium or potassium ions. This addresses scale formation and the other effects of hard water.

Some water filters, such as water pitcher filters, combine ion exchange resin with other water filter media, like carbon media, to remove substances like metal ions and minerals.

Ion Exchange Process

How Do They Work?

Ion exchange filters use a process that involves the exchanging of ions on a charged resin. Any substance with a charge can effectively be removed with an ion exchange filter.

An ion exchange resin consists of small beads, which are packed with charged ions. As water flows through the resin, ions are collected in the resin, and equal amounts of the stored irons are released to balance water’s charge.

Once the resin becomes saturated with unwanted ions, it’ll need to be backwashed or replaced.

4) Membrane Filters

The most commonly found membrane filter is a reverse osmosis system. Ultrafiltration systems also use membrane filtration to treat water.

Reverse osmosis systems have pores of around 0.0001 microns, while ultrafiltration systems have pores of around 0.02 – 0.05 microns, so they don’t remove as many contaminants.

How Do They Work?

Membrane filters use a process called membrane separation to reject the majority of total dissolved solids in a drinking water supply.

These systems force water under pressure through a membrane. The membrane pores are tiny, and most contaminants are rejected (meaning that they bounce back off the membrane rather than passing through). The rejected contaminants are flushed down a drain with a small amount of wastewater.

Learn more about reverse osmosis systems and ultrafiltration units.

Membrane Filtration Process

5) Sequestration Systems

Sequestration is the process of capturing and isolating specific ions, usually metal ions, to prevent their adverse effects on water quality.

We’ve found that sequestration systems are most commonly used to capture hardness ions like calcium and magnesium, inhibiting their effects and mitigating issues such as scaling.

How Do They Work?

Sequestration systems work by introducing chemical agents, known as sequestrants or chelating agents, into the water.

These agents form stable complexes with metal ions, preventing them from reacting with other substances in the water and forming unwanted compounds or precipitates.

The ions are retained in the water, but they’re unable to have undesirable effects.

Filter Combinations

Different types of water filters can remove different contaminants, and some water treatment systems combine several filter types in a single water filtration system.

For example, water filter pitchers commonly combine activated carbon filters and ion exchange resins to allow for more thorough water filtration. Some also use layers of mechanical filtration to reduce additional contaminants.

Springwell cf whole house water filter catalytic carbon and kdf media

How Do They Work?

Water flows through each layer of filtration media, which use their own filtration processes to address specific contaminants.

In a filtration system that uses multiple filters, each filtration media is housed in a different media. Otherwise, the different materials are combined inside the same filtration cartridge.

πŸ“„ Other Types of Water Treatment Systems

There are other water treatment types that are often labeled as water filter systems, including:

  • UV purification systems – UV purifiers treat water with ultraviolet light, which damages the DNA of bacteria, viruses, and other microorganisms, preventing them from reproducing.
  • Water distillation units – The water distillation process works by boiling water until it evaporates, then condensing it into a separate container. The majority of the water’s impurities are left behind in the boiling chamber.
  • Oxidation & filtration systems – Oxidation systems oxidize certain contaminants (typically iron, manganese, and sulfur) with the use of chemicals, oxygen, or other oxidizing formulas. They then remove these contaminants with a filtration media, such as birm or manganese greensand.
  • Remineralization filters – These filters use calcite or mineral beads to add minerals to water. Reverse osmosis units often use mineralization filters to reintroduce the minerals that were reduced in the RO process. Alkaline water pitchers also use mineralization media to boost water pH and improve its taste.

πŸ“‘ Final Word

If you’re new to the world of water filters and you wanted to know how the most common filtration systems work, we hope this guide served as a helpful resource and answered all the questions you had.

We aimed to provide only the information you need to know upfront, but we have plenty of additional guides if you want to deepen your knowledge of water filters or learn if it’s worth it to filter your water.

We’re happy to answer your specific questions, so leave a comment and we’ll get back to you soon!

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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