5 Types of Water Filters and How They Work

Learn about the most common types of water filters and how they work to help you make an educated decision about which water filter makes the most sense for your home.

By: Aditi Pai

Making choices is stressful, but sometimes a selection, like picking out a loaf in the bread aisle, can only steer you so wrong. While other times, like choosing a water filter for your home, the decision is critical.

No one wants to spend money on a water filter only to find out that the filter solves a problem they don’t even have. And yet, when faced with the multitude of water filtration options, it can feel intimidating to find the right one for your home – the one that not only makes your water taste great but also rids it of the maximum number of contaminants.

Fear not. It is simpler than you think. Below is a breakdown of the most popular types of water filters on the market to help you make an educated decision about what water filters make the most sense for your home.

What is a water filter?

Water filters remove or reduce the presence of harmful contaminants in water such as bacteria, chlorine, sediment, and heavy metals. They can improve the taste, odor, and safety of your tap water. However, some water filters are more effective than others when it comes to removing certain contaminants due to the effectiveness of the filtration method they rely on.

The different types of water filters

Depending on what contaminants you want to remove from your water, there are five types of water filtration systems to know about:

  1. Activated carbon
  2. Ion exchange
  3. Reverse osmosis
  4. Mechanical
  5. Ultraviolet

Before delving into the nitty-gritty of each one, there’s one important fact to keep in mind: it’s incredibly important to diagnose the “problem,” or in this case, assess the existing quality of your tap water before choosing a filter. Tap water varies by region, and depending on its source, it could be treated for any number of contaminants. The Environmental Working Group (EWG) has a helpful resource for anyone looking to learn about their water, called the Tap Water Database. It’s a great place to get a basic understanding of your local water quality.

Now, here’s an overview of how each water filtration method found in different types of systems works, including what contaminants they remove.

Activated carbon

Activated carbon water filters reduce chlorine, chloroform, agricultural chemicals, organic substances, sediment, and magnesium.

The key to understanding how an activated carbon water filter works is adsorption. As opposed to absorption, in which one material will take in or soak up another material, adsorption occurs when one material sticks to another while passing through. This is the basis of activated charcoal or activated carbon.

Activated charcoal is created when organic material with high carbon content (like wood, coal, or coconut shells) is heated in such a way that it does not burn, but instead results in char. The char is then treated to create a porous material that binds to certain toxins and impurities, thus pulling them out of the water flowing through the system.

This is the most common type of filter and is often used in conjunction with other filtration methods for maximum toxin removal. Aquasana Whole House Filter Systems, for example, are activated carbon filtration systems that incorporate a salt-free water conditioner, copper-zinc and mineral stone, and UV for maximum filtration.

Ion exchange

Ion exchange water filters are good for the removal of hard water minerals and radioactive material, as well as reducing lead.

As the name suggests, ion exchange filters consist of a substance that will exchange one ion for another as water flows through it. For example, ion exchange will replace calcium or magnesium ions, which cause water hardness, with sodium ions. This will “soften” the water. A home may be experiencing hard water if its water leaves stains on washed dishes. Hard water tends to build up in pipes, which may decrease the life of certain kitchen appliances.

Although ion exchange helps with hard water and some radioactive material, the filter does not remove organic material, particles, or bacteria as effectively as other filtration options. As a result, it should be noted that ion exchange is more commonly associated with water softeners than filters, though softeners may be included as a stage in whole house filters.

Reverse Osmosis (RO)

Reverse osmosis water filters are good at effectively removing a high percentage of toxins including fluoride, hexavalent chromium, arsenic, nitrates/nitrites, copper, radium, salt, and more.

Talk about a good bang for your buck – reverse osmosis filters are incredibly popular for a very good reason. Reverse osmosis filters are top of the line for removing a large percentage of contaminants from the water, potentially including dangerous bacteria associated with waterborne diseases.

RO filters work by pushing water through the reverse osmosis membrane using pressure. The contaminants remain on one side of the film while fresh water is pushed to the other side. It’s one of the few filters that can rid water of water-soluble contaminants like fluoride and chromium +6. If a home has a water softener, an RO system will also remove the salt from drinking water.

While these are becoming a popular option, reverse osmosis systems use an inordinate amount of water when going through the filtration process – sometimes up to four times the normal amount. The process is also slow, causing a decrease in water pressure. That’s why whole-home reverse osmosis systems typically don’t exist. Further, the level of filtration isn’t necessary for day-to-day activities like flushing toilets, taking showers, and doing dishes. Learn more about the pros and cons of RO here.


SmartFlow® Reverse Osmosis

High-efficiency reverse osmosis system removes up to 99.99% of 90 contaminants, including fluoride, arsenic, chlorine, and lead.


Mechanical water filters are good for the removal of physical particles such as sediment or dirt and waste matter.

Mechanical filters are most often used as a pre-filtration method. They work as a barrier where water flows through a mechanical filter and waste material will get stuck between nylon floss, synthetic foam, or in pads. For example, in the case of a fish tank, the filter will trap plant materials, leftover fish food, and waste without trapping beneficial bacteria that are good for fish.

You may notice that mechanical filters have micron ratings which indicates how effective they are at removing certain sizes of particles. Common ratings include:

  • 5 micron: Removes most particles visible to the naked eye.
  • 1 micron: Removes particles too small to see with a microscope.
  • 0.5 micron: Removes cysts such as giardia and cryptosporidium.


Ultraviolet water lamps are a type of home water treatment system that’s good for the removal of bacteria and viruses.

An environmentally friendly option, UV filters will sterilize water using different frequencies of ultraviolet light.

UV filters work using UV light,UV light, which essentially sterilizes all bacteria and viruses when it’s absorbed into their DNA, thus sanitizing drinking water. It’s important to note that UV filters only rid water of bacteria and viruses so it’s important to use this filter in conjunction with other types of filters to remove prevalent contaminants like chlorine, lead, and pesticides, leaving you with clean, drinkable water.

Which filter is best for drinking water?

The best type of water filtration system will depend on which contaminants are in your tap water, as each type of water filter removes different contaminants. The good thing is many water filters on the market use a combination of different filtration methods, as each filter can only remove so much on its own. For example, reverse osmosis systems often use mechanical, adsorption, and then reverse osmosis. If you’re still unsure of which type of water filter is best for your home, check out our guide on how to choose a water filter.