How Water Filters Work: Our In-Detail Guide

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Last updatedLast updated: April 25, 2021

With tap water, you rarely know what to expect. It may have been purified before being distributed to your home but what you sometimes end up with is bad-tasting cloudy water that stinks. This can make the water undrinkable, but there is a solution in terms of a water filter.

Notably, if you fit such filters under your sinks or in the main water connection to your house, the result is clearer, odorless, and great-tasting water. These results may vary depending on the type of filter you’re using. With information on how water filters work, you can determine which one would be the best option for your home, depending on the issues with your water and the results you want to achieve.

5 types of water filters

We already mentioned that there are different types of water filters in the market. They include reverse osmosis filters, activated carbon filters, ion exchange filters, and finally, distillation filters. Notably, they have varying effects on the water-based on how they work.

This section will discuss how each of these filters works and the types of filtration jobs they are perfect for. As a side note, some of the options you encounter on Amazon, other vendor sites, or at your local store incorporate more than one of these filtration systems in their designs.

Reverse osmosis system

How Water Filters Work: Our In-Detail Guide

You may know about osmosis which is a process by which a solvent moves from a less concentrated solution to one that’s highly concentrated. As long as there is a semi-permeable membrane between the two solutions, this process will continue until both solutions are equally concentrated.

Each solution consists of a solvent and a solute.  The solvent, in this case, is the water, while the solutes are all the substances and impurities dissolved in the water that make it more concentrated and less drinkable. Notably, osmosis occurs naturally and doesn’t use up any energy.

On the other hand, reverse osmosis is a process that is initiated by a machine and requires the use of energy. You still have the water solution and a semi-permeable membrane to work with. However, in this instance, the machine will use energy to push water through the membrane.

Since the membrane does not allow most of the solutes to go through, the resulting water is free of some impurities and solutes, e.g., magnesium and calcium ions. Some of the reverse osmosis systems include other filtration systems in their designs as well. This ensures the water reaches a purity level that’s not achievable by using only an RO system.

Additionally, by adding something like a mechanical filter, the semi-permeable membrane in the RO system can last longer.

Activated carbon filter

Activated carbon filters are also known as absorption filters in some circles. These filters use the process of adsorption to their advantage, which is the adhesion of impurities to a surface. Notably, carbon is highly porous, and that allows for water to pass through easily. Additionally, this also means that carbon has a large surface area on which the impurities can get trapped.

Activated carbon is usually treated to have a higher surface area than ordinary carbon. In fact, the surface area can range anywhere from 500m²-3000m² depending on how well it was treated. As such, it will be more effective at latching onto those impurities as the water passes through.

In addition to chlorine, your activated carbon filter will also eliminate herbicides, pesticides, and some of the organic contaminants in your water. The water passed through filters with activated carbon tends to be odorless and tastes better than untreated water.

Another thing that your activated carbon filter might help you get rid of is lead. This is a common problem if there is old lead plumbing providing you with the water in your home. If you drink said water, some of the health problems you may encounter include hypertension, increased blood pressure, problems with your kidneys, and finally, reproductive problems.

The activated carbon attracts lead like a magnet. This is in addition to other volatile organic compounds in the water that might be just as toxic. The Filtrete Maximum 3US-MAX-S01 is, according to experts and reviewers, one of the best activated carbon filter options for removing lead from water. It is an under-sink option that is easy to install and perfect if you get your drinking water from the tap. Additionally, it removes chlorine, microbial cysts, plus particles that are 0.5 microns in size or larger.

Typically the activated carbon filters come in two configurations. One is the granular option, while the alternative is the carbon block option. The latter is more effective and thus more expensive.
Additionally, it should have a micron rating to tell you the size of impurities that it will capture.

While the surface area in activated carbon is large, it isn’t infinite. As such, at some point, the filter will fill up with impurities and will no longer be able to do its job. It is at this point that it should be replaced. Since there is no way for you to check whether the activated carbon filter is full, you should check the manufacturer’s instructions on how long the filter is expected to work.

How Water Filters Work: Our In-Detail Guide

Ion exchange filters

In high-temperature water applications, such as making coffee or even showering, limescale can be a huge problem. It also causes blockages in old pipes. One of the effective countermeasures against this is ion exchange filters.

They eliminate the limescale-causing elements, e.g., magnesium and ions, and substitute them with sodium or hydrogen. This applies to general applications, although sodium ion exchange filters are not recommended for drinking water. The reason is that they tend to impart a lot of salt into the drinking water even past acceptable legal levels.

They can, however, be safely used in applications where you’re not ingesting the water. Worth noting is that these filters are fitted with ion-exchange resins that do all the heavy lifting. These resins will eventually lose their effectiveness, and while it is possible to recharge them, most people would opt to replace the entire filter instead.

Hydrogen ion exchange filters don’t seem to have a salt problem and thus are usable for drinking water.

How Water Filters Work: Our In-Detail Guide

Distillation filters

When boiling water, you eliminate some of the contaminants in drinking water by killing the bacteria and other living organisms. Also, the limescale will tend to harden and settle at the bottom the more you heat this water. The filters take advantage of the fact that most of the solutes and chemicals in the water boil at a higher temperature than the water.

They heat the water to boiling point which kills the bacteria. Also the water starts to evaporate. The steam rises and leaves the solutes in the first container. The steam is then cooled and deposited in a secondary container in the form of pure water.

Unfortunately, while this is effective, some impurities have a lower boiling point than water. This means that ultimately they will find themselves in your drinking water as well.

How Water Filters Work: Our In-Detail Guide

Mechanical filters

Mechanical water filters seem like the simplest of the bunch. They work in the same way a sieve does when you’re using it in the kitchen. Simpler configurations of the mechanical filter include a mesh that can filter out large debris.

On the other hand, some options come with ceramic filters that hang on to pathogenic microorganisms while letting water molecules pass through. The ceramic filter option is, of course, more expensive. Also, these mechanical-type filters tend to have a micron rating, just like the activated carbon filters. This will tell you just how effective each option is.

The smaller the micron rating, the more effective a filter is. For example, a 5-micron rated filter will only work against large particles that you can see with your eyes. Alternatively, one with a 0.5-micron rating should work even against microbial cysts.

How Water Filters Work: Our In-Detail Guide

How do refrigerator water filters work?

If you want clean, clear water in your ice cubes or when you use the through-door water dispenser in your fridge, it’s a good idea to install a water filter. Some are made specifically for that purpose, and you can easily find them on Amazon.

The EveryDrop by Whirlpool EDR3RXD is, according to users, a very effective refrigerator water filter as it can remove lead, parasites, pharmaceuticals, and even pesticides from your water. It also comes approved by several brands to give you a little bit of extra assurance.

So how do refrigerator water filters work? Well, most of them are fitted with activated carbon filters. As such, they work on the basis of adsorption and can get rid of chlorine, pesticides, and lead in addition to other impurities in the water.

Again, it’s imperative that you replace the filters at the intervals suggested by the manufacturer; otherwise, you’ll end up drinking water with the impurities that you’re trying to avoid.

How do whole house water filters work?

Admittedly most of the whole house water filters work using activated carbon, although another filtration system might also be included in the device. These are recommended since most of us use water from municipal systems. That means that the water has already been treated with chlorine to remove some of the impurities. However, some of those that remain, including the chlorine itself, can be removed by the activated carbon.

There are two major types of whole house filters that you find in the market. One is the standard capacity water filter. These tend to last about a year before they need to be replaced. They are cheaper to acquire, and this is one reason they are preferred over the alternative.

According to reviewers, the iSpring WGB32B 3-Stage water filter is one of the best standard capacity whole house water filters in the market. As implied in the name, it has three stages of filtration. The first uses a mechanical filter to get rid of any particle that is 5 microns or larger. The second and third stages are both activated carbon filters.

The second major type of whole-house water filter is larger and provides you with contaminant protection for a longer period. Most options give you between 5 and 10 years of service before you have to replace the filter media.

How do portable filters work?

The question of how portable filters work does not have a single answer. Instead, the answer will depend on the model and type that you picked. One will use reverse osmosis while another will use activated carbon or a mechanical filter. However, we’ve already covered how each of these operates in the sections above. Use them as a reference point once you know more about the type of filter you’re eyeing.

How do UV water filters work?

The last type of filter we’ll be covering is the UV option. So how do UV water filters work? Well, they incorporate germicidal lamps, which produce UV-C light. Notably, the light is capable of disrupting DNA base pairing in bacteria, viruses, and protozoa. The resulting inactivated contaminants can therefore cause you no harm as you drink the water.

The light runs on battery power, and thus you’ll need to replace the batteries now and then. Unfortunately, the only things that UV filters are capable of eliminating are living microorganisms. This means that substances like lead, chlorine, debris, and more will be left in the water. For this reason, it’s recommended that you pre-filter the water using a different system, e.g., distillation, mechanical, or reverse osmosis system, before you pass it through a UV filter.

Final thoughts

As you can see, how water filters work will depend on the type of filter media used. That said, most of the options in the market don’t just incorporate one type of filter media. Instead, you’ll find a combination of activated carbon with mechanical or ion exchange filter media in the same device. This will increase the effectiveness and make sure the water you’re drinking is pure and clean.

Also, as you’ve seen above, each type of filter media effectively removes different kinds of impurities. Some work best for living microorganisms, others for limescale, and others for chlorine and chemical solutes.

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