How Do Water Filters Work? | Complete Guide by Illi Water

Water filters are essential for most households in Canada and around the world. If it weren’t for these, we wouldn’t have easy access to the clean and refreshing water we use for drinking, cooking, showering, cleaning, and whatnot. But how do water filters work, really? 

Understanding how filters function is important for homeowners to choose the right filter for the specific contaminants in their water, avoid wasting money on inappropriate technology, and stay on top of routine maintenance. This guide explains how water filters work, the contaminants they remove, and the different mechanisms they employ to purify water.

Key Takeaways

1. Water filters employ 4 main mechanisms to remove impurities: chemical filtration, physical filtration, membrane separation, and biological treatment.
2. Different water filters address different concerns. For this reason, multi-stage filtration systems are often the most effective solution.
3. Based on the technology used, common household filters remove suspended particles, heavy metals, bacteria, and chlorine from the water.
4. Reverse osmosis (RO) systems deliver comprehensive water purification by removing up to 99% of total dissolved solids (TDS), chlorine, heavy metals, hardness minerals, and other impurities. 
5. While municipal water is treated, contaminants from aging pipes can seep into it.
6. Understanding the steps of water filtration helps you get the right system and also maintain it well.

What Is a Water Filter?

A water filter is a system or device that removes unwanted and harmful substances from water to improve its safety, clarity, taste, smell, and overall quality. Water filters work by passing water through special barriers, materials, or membranes that block, trap, or absorb impurities. Depending on the technology a filter uses, it can remove chemicals, heavy metals, hardness minerals, microorganisms, and sediment.

While the filtration process varies by system, the goal remains the same: cleaner, more hygienic water. To better understand how filters achieve this, it’s helpful to first differentiate among filtration, water softening, and purification.

Water Filtration vs. Purification vs. Softening: What’s the Difference?

Although these terms are used interchangeably, filtration, purification, and water softening refer to distinct stages of the water filtration process.

Water filtration 

It refers to the removal of physical and chemical contaminants by passing water through materials such as activated carbon, membranes, or sediment. Carbon media absorbs chemicals like pesticides and chlorines, whereas membranes and sediment filters trap particles such as rust, sand, and other impurities.

Water purification: 

It targets biological threats, including bacteria, viruses, and parasites. Technologies such as distillation, ultraviolet (UV) disinfection, or ultra-fine membranes neutralize these organisms by damaging their DNA.

Water softening: 

It focuses primarily on removing hardness from water. It employs ion exchange technology to swap the hardness minerals, such as calcium and magnesium, with sodium or potassium.

Most water filtration systems combine two or more filtration approaches to effectively filter, purify, and soften water. One such popular system is the reverse osmosis system from Illi Water, which integrates filtration with purification to address a wide range of water quality challenges.

How Your Water Is Already Treated (And Why You Still Need a Filter)

Water is treated at a municipal facility before it reaches your shower or tap. The standard municipal water filtration process constitutes four main steps:

1. Coagulation, wherein chemicals are used to clump tiny particles of contaminants together
2. Sedimentation, wherein the particles settle out of the water
3. Filtration wherein the leftover debris is trapped
4. Disinfection wherein chlorine is used to kill the toxic microorganisms 
   

Once the process completes, water leaves the treatment plants. Yes, the water complies with regulatory safety standards by that time, but on its way to your home, it can pick up contaminants. 

• While moving through old pipes in the treatment plant or residential plumbing systems, the water becomes contaminated with metals such as copper or lead. 
• Chlorine, typically used to disinfect water during municipal treatment, also affects the water’s taste and odour. Moreover, it often produces disinfection byproducts known as trihalomethanes (THMs) that further deteriorate the water’s quality and safety.
• Additionally, contaminants such as microplastics shed from routine products, pharmaceutical residues from wastewater treatment plants, and PFAS chemicals from firefighting foams and industrial sites make their way into the water. 
• Homes that use private wells face an even greater challenge, as water comes directly from the ground and isn’t treated at a municipal facility. 
  

So even if you have access to municipally treated water, it is not entirely safe from the harms of contaminants and needs to undergo comprehensive filtration. And if you use well water, make sure to properly filter it to make it safe for routine consumption.

Why Understanding How Your Filter Works Matters

Not every water filter works the same way. Different filters use different technologies that tackle different contaminants. Knowing how a filter works helps you pick one that addresses your particular water concerns.

Moreover, knowing how filters work also helps you understand their maintenance requirements. You can then better care for your filter to ensure it functions effectively at all times.

Not sure which system is the perfect fit for your home? Take Illi Water’s quick system quiz to find the best water filtration solution according to your household needs and water source.

What Are the 4 Different Water Filtration Processes?

Every water filter relies on one or more of the four fundamental filtration methods. Understanding them is pivotal to understanding why different filters exist and why the most powerful systems stack multiple approaches.

Below are the four fundamental filtration steps that different water filter systems use:

1. Physical filtration
2. Chemical filtration
3. Biological treatment
4. Membrane separation

Let’s discuss these approaches one by one.

1. Physical Filtration — Blocking Particles by Size

Physical filtration is the most commonly used and simplest type of water filtration. Water moves through a porous material that traps particles based on their size. Particles bigger than the size of the material’s pores are left behind. 

Filters are rated by microns, a measure of their size. For instance, a 5-micron filter captures anything bigger than 5 microns. For context, a human hair is around 70 micrometres thick. Imagine something 70 times tinier—that’s what a physical filter catches.

Sediment and ceramic filters use physical filtration. Moreover, physical filtration is the first line of defense in most multi-stage water filtration processes. It successfully removes visible impurities like dirt, rust, silt, sediment, sand, and even larger microorganisms such as Giardia.

2. Chemical Filtration—Adsorption and Ion Exchange

Chemical filtration eliminates impurities that a simple barrier fails to remove. Typically, it functions through two mechanisms: adsorption and ion exchange.

Adsorption takes place when water passes through an activated carbon block. Carbon has a very porous surface that draws and clumps certain chemicals. As a result, it effectively gets rid of chlorine, pesticides, volatile organic compounds (VOCs), unpleasant odors and tastes, and even certain heavy metals.

Ion exchange, on the other hand, takes a different approach. It uses special resin beads that exchange unwanted ions or minerals in the water with safer ones. For instance, water softeners switch the magnesium and calcium ions (hardness minerals) with potassium or sodium ions.

3. Biological Treatment—Neutralizing Living Organisms

Biological treatment neutralizes the living contaminants in water. Ultraviolet (UV) disinfection is a commonly used biological treatment method in households

During UV disinfection, water flows through a UV lamp (commonly referred to as a bulb) that produces a germicidal light that destroys the DNA of bacteria, viruses, and other parasites in the water. With their DNA damaged, the microorganisms become infertile and can no longer reproduce.

While UV treatment does incapacitate the microorganisms, it doesn’t filter out any chemicals or particles. Due to this limitation, it is best to pair it with other filtration stages to comprehensively treat water.

4. Membrane Separation—Reverse Osmosis

Membrane separation, particularly reverse osmosis (RO), is among the advanced water filtration technologies. The filtration process steps include applying pressure on water to force it through a semi-permeable membrane with microscopic pores as small as 0.0001 micrometers. Due to their small size, they block every impurity except the water molecules.

RO filtration systems are effective at removing up to 99% of dissolved solids such as fluoride, salts, nitrates, heavy metals, and chemical impurities. They flush away the impurities, delivering ultra-pure drinking water.

Traditional RO systems using older technologies produce a lot of wastewater to purify water. The typical ratio of wastewater to pure water is 3:1 or 4:1. However, modern RO variants employ cutting-edge technology that allows them to reduce the production of wastewater. 

Systems such as IliWater’s advanced reverse osmosis water filters have a higher efficiency with a drain-to-pure ratio as low as 2:1. As a result, they save thousands of liters of water every year compared to their older counterparts.

What Do Water Filters Remove?

What a water filter removes depends on the technology it uses. Let’s walk you through the main contaminant groups and the filtration methods that handle each type.

Physical Contaminants (What You Can See)

Physical contaminants are all the visible particles that impact the water’s clarity. Generally, these comprise silt, sand, dirt, rust, and sometimes manganese or iron particles that can stain your fixtures and appliances. Physical filtration that generally uses sediment or ceramic filters removes all these impurities.

Quick Test To Check If Your Tap Water Has Physical Impurities

Your home water contains physical contaminants if

• Your tap water often appears cloudy
• Tap water leaves stubborn stains with a brownish or orange hue on your fixtures 

Chemical Contaminants (What You Can’t See)

If your home water doesn’t appear cloudy or stain your appliances, great! But that doesn’t mean it is pure. Many contaminants are invisible. These include:

• Chemical contaminants, such as chlorine and chloramine, affect the odor and taste of water
• Heavy metals such as arsenic, lead and mercury that can cause long-term damage to your brain, kidneys and the nervous system
• Herbicides and pesticides that disrupt hormonal balance, and harm your nervous and reproductive systems
• Volatile organic compounds (VOCs) that can damage your kidneys, central nervous system, and liver over time
• Nitrates that affect your blood’s oxygen-carrying capability
• Fluoride, which is beneficial in small amounts, but excessive exposure can weaken joints and bones
• Total dissolved solids (TDS), which at high levels impact the water’s taste, and also indicate the presence of other toxic impurities

Advanced water filters can tackle all these contaminants. Activated carbon filters do a great job at eliminating VOCs, chlorine, and chemicals that give water a foul taste or smell. However, carbon falls short of removing nitrates, fluoride, and TDS. That’s where the membrane-based technologies come in handy.

RO filtration systems effectively remove a broad range of dissolved substances and chemicals. That’s exactly why many cutting-edge multi-stage systems combine RO and carbon for comprehensive filtration.

Biological Contaminants (What’s Living in Your Water)

Typically, biological contaminants are microorganisms that consist of the following:

1. Bacteria such as coliform or E.coli
2. Parasites such as Giardia and Cryptosporidium
3. Certain viruses
   

Microorganisms tend to creep into water through untreated well water, aging infrastructure, and natural sources. UV disinfection is a reliable method to eliminate microorganisms from water by crippling their DNA. RO membranes with ultra-fine pores can also block many biological impurities.  

But standalone carbon filters are ineffective in treating parasites or bacteria. Basic pitcher filters generally employ carbon blocks that improve the water’s taste but fail to protect it from biological contamination.

Quick Reference: Which Method Removes What?

The table below gives a quick summary of the best filtration technology for specific contaminants.

How Each Type of Water Filter Works

Now that you have an understanding of the four core filtration methods, it’s easier to see how real-world systems put them into action. Different water filtration systems integrate these processes practically to address specific contaminants. All the filters below use one or more stages in the water filtration process to remove specific impurities, each with its own strengths and limitations.

Reverse Osmosis (RO) Systems

Reverse osmosis is deemed the most comprehensive technology employed in advanced water filtration systems. An RO system pushes water under pressure, so it passes through a semi-permeable membrane with extremely tiny pores (0.0001 microns) that block up to 99% of impurities while allowing water molecules to pass through.

Most RO systems used in Canadian homes are multi-stage. The first stage is usually a sediment pre-filter that traps dirt, silt, rust, and sediment, followed by a carbon stage that removes chlorine that could damage the RO membrane. Next, the RO membrane blocks heavy metals, nitrates, fluorides, dissolved solids, and other contaminants. The process ends with a post-filter that refines the water’s taste and smell. Some systems also contain an additional layer of UV disinfection.

RO systems are best at removing a broad spectrum of contaminants, delivering clear, delicious, and healthy drinking water. They do have a limitation, though: they produce 3 to 4 gallons of wastewater to purify 1 gallon of water. That said, modern systems like the Illi Water RO system have a much higher efficiency with a drain-to-pure water efficiency of 2:1. Moreover, it carries NSF/ANSI certification and has a straightforward under-sink installation.

Mechanical (Sediment) Filters

The simplest types of water filters, mechanical or sediment, use a physical barrier, generally ceramic, wound polypropylene, or mesh, to trap visible impurities based on their size.

Mechanical filter cartridges are rated in microns, which represents the particle size they can capture. For instance, a 1-micron cartridge can trap particles larger than 1 micron in size. 

They do quite a thorough job at filtering out all suspended particles from the water before it reaches your tap. However, they are fit to only remove the visible contaminants and cannot eliminate biological, chemical, and unwanted mineral contaminants. For this reason, they are installed as the frontline protective layer in most multi-stage water filtration systems.

Activated Carbon Filters

Activated carbon filters are widely used in household water filters. In Canada, around 70% of all water treatments sold contain activated carbon filters.

Water passes through a block of highly porous carbon, generally made from coal or coconut shells, that attracts and binds together certain impurities to its surface. These impurities include chlorine, chloramines, VOCs, pesticides, and other chemicals that add an unpleasant taste and smell to the water.

Carbon filters do have their own constraints. They are incapable of removing TDS, bacteria, nitrates, fluoride, or dissolved minerals. Secondly, they exhaust within a few months and demand frequent replacement to work effectively. This is why they are better off as a filtration stage in multi-stage filters rather than as standalone solutions.

Ion Exchange Filters

Ion exchange filters replace certain ions in the water (those that adversely affect it) with less problematic ions. They contain resin beads bearing an electric charge that attract specific minerals and swap them with better substitutes.

Water softeners are the most commonly used type of ion exchange filters. They switch the calcium and magnesium ions (responsible for causing hard water) with potassium or sodium ions. Water becomes soft and doesn’t produce scale that harms your appliances, fixtures, and plumbing.

If you get hard water in your house, ion exchange filters are the best treatment for it. Plus, they can also eliminate certain dissolved metals. While they are incredible at treating hard water, they don’t filter chemical pollutants, biological contaminants, or sediment. Precisely why they are installed as point-of-entry (POE) systems integrated into your main water supply to treat hard water and not purify it.

Ultraviolet (UV) Filters

UV filters shield water against biological impurities. Water passes through a chamber containing a UV bulb that emits germicidal light at 254 nanometers. The light disrupts the RNA or DNA of the microorganisms, keeping them from reproducing. UV filters do not introduce any chemicals into the water, making it biologically safe for consumption.

That said, they can only neutralize living organisms and don’t remove sediment, hardness minerals, or chemicals from the water. Moreover, the water must be crystal clear for UV light to work effectively, as suspended particles can shield microbes from its effects. 

Because of this, UV disinfection is employed as a pre-filtration stage in multi-stage filters. Illi Water offers UV filters as an optional add-on to its RO systems for enhanced protection.

Ceramic Filters

Ceramic filters use a porous ceramic cartridge that serves as a physical barrier to filter water. Water flows through the ceramic material’s microscopic pores that screen out parasites, bacteria, and sediment.

Certain ceramic filters are coated with silver to inhibit bacterial growth on their surfaces. These are common in portable or gravity-fed filters. Despite protecting against microbes, they fall short of removing minerals or dissolved chemicals from water. 

Additionally, they require periodic manual cleaning to operate optimally, as trapped particles often accumulate on their outer surfaces.

Ultrafiltration (UF) Membranes

UF membranes rely on advanced membrane technology with pore sizes ranging from 0.01 to 0.1 microns. Their pores are so fine that bacteria, viruses, and parasites cannot pass through. But they retain the water-soluble minerals, ensuring it stays nutritious for drinking and cooking.

A major advantage of UF systems is that they don’t waste water like RO units do. That’s why environmentally conscious homeowners prefer using them. But they leave behind heavy metals, TDS, hardness minerals, and dissolved chemicals. That explains why they are commonly paired with other filters to remove a wider range of contaminants.

How Multi-Stage Water Filtration Systems Work (And Why They’re More Effective)

Well water and even municipally treated water are infected with several impurities. Typically, the water supply in most households is packed with chemical residues, microscopic organisms and sediment. To tackle this, modern water filtration units used nowadays depend on two or more filtration approaches to comprehensively treat water.

Multi-stage systems address this complexity by combining several filtration steps, with each layer attacking a specific type of impurity. With this layered approach, your water quality improves substantially.

Why No Single Filter Does Everything

The truth is no single filter can eliminate every contaminant found in water. Every method we have discussed in this read comes with its fair share of strengths and limitations. 

Sediment filters can’t remove dissolved chemicals, carbon filters are ineffective against bacteria, and UV systems don’t work on chemicals or visible particles. While RO membranes are super-powerful, chlorine can damage them if the water isn’t pre-treated.

These limitations clearly show why water filters need to work together like a fortified team to properly treat water.

How a Typical Multi-Stage RO System Works (Stage by Stage)

A reverse osmosis filtration unit is an excellent example of a robust multi-stage filter. Let’s give you a breakdown of the different steps of water filtration in this process:

• Stage 1—Sediment Pre-Filter: As water flows through it, the filter traps rust, sand, silt, and other suspended impurities. It also shields the more sensitive downstream stages.
• Stage 2—Carbon Pre-Filter: It clears out chlorine (that is damaging to the RO membrane), chloramines, and unwanted tastes and odors.
• Stage 3—RO Membrane: This is the core stage that eliminates up to 99% of TDS, fluoride, heavy metals, and other harmful substances from the water.
• Stage 4—Post-Carbon Polish: It gives water a nice polish to refine its taste.
• Optional—UV Disinfection: An optional layer of UV filter removes biological impurities from the water.
• Optional—Remineralization: It reintroduces minerals such as calcium and magnesium (they are incapable of turning the water hard at this point) in the water to make it healthier.

Illi Water’s cutting-edge RO systems exercise this exact approach. You can also personalize a 4-stage filter with 5 or 6 additional stages to align with your water profile and household needs.

City Water vs. Well Water: Different Starting Points, Different Needs

Your water source plays a significant role in determining which water filter is best for your home.

City or municipal water is pre-treated before reaching households. Treatment plants use chlorine to disinfect water and often add fluoride to it. Home filtration systems need to focus on eliminating disinfection byproducts such as THMs, chlorine taste, emerging contaminants such as PFAS, and residual metals that leach from old pipes. Multi-stage RO systems are well equipped to address these concerns.

On the contrary, well water doesn’t undergo any municipal treatment and is therefore more harmful. Homeowners need to purify their own water of sediment, bacteria, hardness minerals, nitrates, and heavy metals. In such a scenario, it is essential to get at least a sediment filter paired with an RO or UV filter.

Irrespective of your water source, get your water professionally tested first. The assessment reveals the exact contaminants in your water, enabling you to select the best filtration solution.

FAQs

Do water filters really purify water?

Whether a filter can purify water or not depends on its type. Basic carbon filters primarily improve the water’s taste. While they remove certain chemicals, they don’t completely purify water. However, multi-stage RO systems can eliminate up to 99% of contaminants, including TDS and bacteria, which does qualify as true water purification.

Do water filters remove good minerals?

Some filters, like the RO systems, remove most dissolved substances, including beneficial minerals such as calcium and magnesium. However, we do get these minerals from food. Many advanced water filters have an additional remineralization stage that adds back the healthy minerals for improved balance.

How often should you replace a water filter?

Replacement schedules depend on the filter type. Sediment filters can last for 3 to 6 months. Carbon filters need replacement every 6 to 12 months. RO membranes stay strong for 2 to 3 years. And UV bulbs last for about a year. Your household usage and water quality directly affect the filter’s lifespan. Make sure to adhere to the manufacturer’s guidelines.

Can a water filter make tap water as good as bottled water?

Yes. Multi-stage RO systems produce water that meets and sometimes even surpasses the standards set by most bottled water brands. In the long run, having a water filter costs far less than buying bottled water.

Do water filters waste water?

Some water filters waste water. RO filters produce wastewater to generate clean water. While older variants waste four to five gallons of water to produce one gallon of pure water, modern systems are more efficient and waste far less water.

Is filtered water safe for babies and pets?

Yes, filtered water is clean of heavy metals, microbes, chlorine, and other harmful contaminants, which makes it safer for pets and babies as compared to untreated tap water.

Do I even need a water filter if my city water is already treated?

If your water tests clean and you are satisfied with its taste, you don’t really need a water filter to treat your city water. However, once the city water leaves the municipal plant, it can accumulate contaminants. It is best to get a professional water test first and then decide about getting a water filter.

The Bottom Line: No Single Filter Does Everything

Now that you are well aware of how water filters work, you understand that each filtration technology addresses only specific impurities. Be they carbon, sediment, ORO, or UV filters, each has its own shortcomings. That’s why it is best to invest in a multi-stage water filtration system that comprehensively treats water against every possible contaminant.

That said, a wise move is to get a water test first and analyze your household’s water usage. Once you know your water quality and needs, you can choose the best system accordingly. And you can also take IliWater’s quick system quiz to figure out the perfect system for your home.