How Do Water Filters Work?

How do water filters work?

We need clean water to live. Clean water is hard to come by, and even if you live by a clean source of freshwater, like a mountain stream, your water is likely touched by some kind of treatment or filtration system before it goes through your taps.

Most water needs to be filtered (cleaned) in order for us to drink it. This is done by “filtering” or separating and removing harmful bacteria and chemicals from the water.

People living in cities and large towns often have filtered water coming through their taps. Still, people who don’t like the taste of their water, or simply want to clean their water thoroughly may use filtration systems at home, too.

Water is often filtered before it comes through our taps, but if it isn’t, or if we prefer to filter our water again, we can use water filters at home.

Water Filters Have a Few Purposes

  • Removing harmful chemicals and bacteria (“impurities”) from water, making it drinkable
  • Changing the taste of water
  • Softening water

Removing Impurities

Water filtration removes harmful chemicals and bacteria from our water so we can drink it an bathe in it without any problems. These harmful chemicals and bacteria are called “impurities.” Water doesn’t need to be completely free of bacteria for it to be drinkable, but a certain amount needs to be removed.

Usually this type of filtration is done before the water goes through our taps, especially if we live in a large town or city. People who access well water or other sources of water may need to filter their water in order for it to be drinkable.

Changing Taste

Water filters can also be used to change the taste of the water. Some people dislike the taste of tap water, and use water filtration systems at home to already filtered water.

Softening Water

Another function of some water filters is to “soften” water. People living in places where elements like calcium and iron are common have “hard” water most often. This is because the water source comes into contact with them and is carried through to the tap water.

Hard water usually creates a crusty buildup on our taps and showerheads. It can also taste different than soft water. Some people don’t like these effects, and can use a water filter to soften the water.

So how do water filters work?

Two Types of Water Filtration

The process of water filtration can be done in two ways:

  • Physical filtration:

    • creates a barrier that clean water will flow through, but that purities will become caught up in, unable to pass through
  • Chemical filtration

    • water is mixed with a chemical that removes impurities

Types of water filters

There are many kinds of water filtration systems. The most common found in the home include:

  • Activated carbon
  • Reverse osmosis
  • Ion exchange
  • Distillation

Activated carbon/Sand filter

If you have a jug of water in your fridge with a water filter, it probably uses this system. Activated carbon granules (think about a grain of sand: that’s a granule) are made of charcoal.

The grains of charcoal have lots of small holes in them that allow the water to flow through, but not the impurities.


Activated carbon water filters are great at removing impurities found in the water we use everyday at home. For example, these water filters easily remove the chlorine-based chemicals that are used to treat wastewater before it makes its way to our water taps.


These water filters don’t work well for larger impurities. For example, if you have hard water, these water filters won’t be able to remove the hardness from the water.

Reverse osmosis

How Do Water Filters Work

This sounds complicated, and it is, but it can be easily explained: similar to the activated carbon water filter, reverse osmosis filters water by pushing it through a membrane (filter) using pressure. This, again, allows the clean water to flow through and the impurities to be removed, as they can’t pass through the filter.


Reverse osmosis is good at removing the same kinds of impurities as the activated carbon filter, but also larger impurities like limescale (causes of water hardness).


Reverse osmosis can’t remove all impurities, including bacteria. This system uses electric pumps, making it more costly than other kinds of water filtration systems. It also produces a lot of wastewater.

Ion exchange

Ion exchange water filters soften the hard water that leaves buildup on taps. They work by replacing the ions (building blocks of elements) found in elements that contribute to hard water like calcium or magnesium with other ions.

This works in the same way as the other filtration systems noted so far, because, in passing the water through the ion particles, it traps the ions that create hard water and release ions that make the water soft.

This water filter system is different than the others, though, in that it does actually change something about the water by changing the ions from “bad” ions that create hard water to “good” ions that create soft water.


Ion exchange water filters are very good at removing and replacing larger impurities like limescale (residue from calcium and magnesium that cause water hardness).


In order to create the ion exchange, it’s necessary to add sodium into the water filter. The sodium is also a kind of impurity, though, and can still be found in the water after filtration.

Ion exchange water filters also need to be recharged every so often with more sodium. This is done by adding salt.


Water filters that use distillation use a common method of water purification, boiling, but go one step further. Boiling water does a great job of removing harmful bacteria from the water. However, it doesn’t remove other impurities like limescale (cause of water hardness) and chemicals.

Water distillation filters boil the water, then use the steam created by the boiling as the clean water. The steam is captured and cooled. This works because it separates most of the impurities from the water, but not all.


The distillation water filter process creates water that is 99.9% pure.


This water filtration process doesn’t completely clean the water, but comes quite close.


Water filters are important to our everyday lives. Unless we drink directly from a freshwater source that has very little bacteria in it, water filters are necessary to provide the clean drinking water we need to live.

There are many kinds of water filters, and they can serve different purposes. The main purpose of a water filter is to remove impurities in the water. Water filters can also change the taste of water. Another purpose of water filters is to soften the water by removing limescale, which leads to buildup on our taps and shower heads.

Water filters work in different ways, but, as their name suggests, they all work in some way to filter out the water’s impurities and allow only the clean, drinkable water to flow through.


Explain that stuff. How do water filters work?

Wikipedia. Water purification.

Checkout our 10 Best Survival Water Filters 2018 [Review]