We have talked about water purification and how water filters work many times before, but today we want to present you with a short but comprehensive guide on what is water filtration and how the different types of filters and devices can help you enjoy clean, safe water. Let’s see today a few things about the need to use a water filter and how do water filters work!

What is a Water Filter?

how do water filters work

Before we begin discussing the different processes involved in water purification, we should first clear up some things regarding the following:

  • What is a water filter;
  • Do we really need one at home, at the office, or in our business?

Let’s start with a definition within the commercial framework of our analysis (and not necessarily in the framework of industrial water purification systems used by city authorities, plants, and so on).

  • A home water filter is a device designed and built to remove or lower the contaminants in the water using a physical mechanism, a chemical process, etc.

In other words, if you have a product in which you put contaminated water to obtain less or non-contaminated water for your daily needs, that item pretty much qualifies as a water filter.

The discussion regarding the need of water filters in our homes, offices, or businesses is a bit longer, but it is necessary if you want to understand how do water filters work and whether you should invest in one in the foreseeable future.

Water Purification: Is it Really Necessary at Home?

Why do we buy so incredibly many plastic water bottles to quench our thirst and avoid the tap water in our homes or apartments? One reason is that tap water – municipal or otherwise – has a funny taste or smell to it. Most of the times it leaves white spots on the dishes and more often than not it damages the plumbing.

Many people also believe that the water contains heavy loads of contaminants and all sorts of water pollutants.

Moreover, most people don’t realize that plastic water bottles are a serious threat to the planet, as we recycle very little in reality – and that, budget-wise, buying disposable water bottles is tenfold more expensive than drinking tap water.

In short, environmentally conscious people invest in water filters for two main reasons:

Now let’s discuss the safety of our everyday municipal or well water.

The Pollutants in Water: How Dangerous are They?

how do water filters work

According to the EPA, by 2018, 92% of community water sys­tems should have delivered water within all applicable health-based drinking water standards. Nevertheless, people have concerns regarding the water contaminants they ingest. Let’s see what the EPA has to say about the most common water pollutants.

Common Tap Water Contaminants

The list is rather long, unfortunately, and you can consult it on the Water Quality Association’s website, but the EPA categorizes water pollutants in four main categories:

1. Physical Water Contaminants

They have an impact upon the physical properties of water, aspect included. As examples, we can list here:

  • Sediment
  • Suspended organic material

2. Chemical Water Contaminants

In this category, you find most elements that water filters are designed to remove or lower down, a sign that they raise the most concerns. Here are some of them:

  • Heavy metals, bleach, salts, nitrogen, pesticides, bacteria-produced toxins, human/veterinary drugs, and more.

3. Biological Water Contaminants

In this category, we find microorganisms (microbiological contaminants). They include:

  • Viruses, bacteria, parasites, protozoa.

4. Radiological Water Contaminants

Radiological elements are the ones that feature an imbalance in their protons and neutrons numbers, leading to instability that might produce ionizing radiation. Among the most common radiological contaminants you find in the water, the EPA lists:

  • Uranium, plutonium, and cesium.

Since no one can take lightly the idea of having uranium or viruses, fluoride, bleach, or mercury in their drinking water, the need for reliable water filters turned into a trend. Before we begin describing the process of water purification at home, we should, however, discuss TDS – an issue that confuses many people, especially when they want to buy the best water filter on the market and they want to understand better how do water filters work and what type of filter they need.

The Problem of Total Dissolved Solids

If you checked out some of our home water solutions up until now, you noticed that we talked about Total Dissolved Solids (TDS) many times when we reviewed different types of water filters.

As definitions go, Total Dissolved Solids represent a measurement of the amount of the dissolved content of all inorganic and organic substances combined in a liquid. Their form can be molecular, ionized, or micro-granular. For some elements in the water to qualify as TDS, they should be small enough to pass through a 2 (or less) micron filter.

  • When you talk about TDS, you usually talk about freshwater sources. Moreover, TDS’ main application is the determination of water quality.

TDS are not considered a primary pollutant, as they do not pose threats to human or animal health, but they come up in the conversations regarding water aesthetics, smell or taste, as they play the role of an aggregate indicator of the presence of a broad specter of chemicals in the water.

Before you learn how do water filters work and which type of home water purification you need, you should test your water. Now, water testing is a bit tricky, as the kits and diagnosis tools you purchase online or in shops may not be as reliable or as accurate as you might like.

Can You Test Your Own Water?

Yes, but the best practice is to send water samples to a certified laboratory or have some experts come down your house and test the water through validated means.

In the framework of water contaminants as defined by the EPA and TDS, now we can understand better what is water filtration and how water filters work.

How Do Water Filters Work: The Process(es)

Before you ask yourself what is the best filtration system you should buy for your home, you should understand the difference between water filters according to the technology (or process) they implement to remove the water contaminants. While most water filters use a mixed combination of such processes, we can distinguish among five main ones.

1. Adsorption

how do water filters work

A process that involves the presence of one or more activated carbon filters. ACFs are the most common household filters you will find on the market as they are affordable, easy to use, and easy to install, and so on.

  • Adsorption is a process where liquids attract other liquids or solids. When the home water passes through the carbon filter, it will attract most impurities to its surface like a sponge.

The drawback of some carbon filters is that they cannot block limescale and a few other sneakier contaminants (that feel no attraction towards charcoal), like some microbes, fluoride, nitrates, etc.

Before you go searching for the best water filter with activated carbon filters, look at the device’s tech specs and read the reviews. Pay attention to micron ratings, filtration stages, types of combined filters, efficiency, etc. We will resume some of these specs to give you a clearer view of the matter.

Adsorption is one of the most common answers to the question of how do water filters work. You will find this mechanism of water purification in plenty of whole house water filters and faucet filters.

If for faucet filters you need to first check the type of your faucet, as many such products are not compatible with unconventional ones, for whole house water filters you have to take into account their size, weight, and installation guidelines.

Check Out The Best Whole House Water Filters    Check Out The Best Faucet Water Filters

2. Reverse Osmosis

how do water filters work

You may not remember the osmosis definition from biology class, so we will offer you a short reverse osmosis definition to make matters more clear. If you ever asked yourself what is reverse osmosis and how this technology cleans your water, here it is:

Reverse Osmosis Definition

RO is a process through which we purify drinking water by using a partially permeable membrane that removes ions, potentially harmful molecules, and even larger particles.

We have talked about reverse osmosis water filtration before, so we will not insist on the details, but give you an overview of how do water filters work when they rely on this technology.

  • RO systems strip the water of all its impurities, salts, contaminants, and minerals (of a certain size);
  • Not all people favor reverse osmosis system filters because the “clean” water they create is also lacking all health properties;
  • Many reverse osmosis filters brands are quite mindful about the demineralization problem and make sure that at least one or two stages of the process re-mineralize and alkalize the “dead” water with healthy elements in the right concentrations.

3. Ion Exchange

how do water filters work

Ion exchange is a process you will find most likely in water softeners rather than simple water filters, although they work together brilliantly.

  • Ion exchange filters contain zeolite beads full of sodium ions. When hard water passes through, the elements giving it its hardiness, magnesium, and calcium, attract the ions, which release the sodium in the water.

Dealing with hard water is easier and more affordable than dealing with heavily contaminated water, but such problems are not mutually exclusive. On the contrary, as we said, the best way to treat your water at home is to mix the best water filter with one of the best water softeners available on the market.

However, not all people enjoy the taste of soft water (a bit salty, indeed). Some even have health restrictions regarding salt consumption, so they have to find alternatives.

4. UV Filtration

how water filters work

UV water filters are highly efficient when it comes to water sources with high bacterial levels. UV filters, however, use electricity to function. While they do kill almost all bacteria, viruses, and other microorganisms in the water, they do not remove anything else you might have in there.

For this reason, UV filters come as accessories and added elements to whole house water filters working on the absorption principles or other types of filters employing reverse osmosis.

5. Distillation

how water filters work

Distillation is probably the oldest type of water filtration humankind has ever used. We still use it, in a simpler form, by boiling the water to make sure it does not contain active microorganisms or other contaminants anymore.

  • Professional distillation filters, nevertheless, boil the water and capture the condensed steam in another compartment, while removing the contaminants found in the original container.

One of the drawbacks of distillation water filters is that they do not remove all drinking water contaminants (as some of them boil before the water does and reach the second container easily). Moreover, the boiling process does remove healthy minerals in the water. In comparison to a modern reverse osmosis system, the distillation process does not add back the lost minerals.

Most Common Water Filter Systems by Installation

Now that we saw how do water filters work depending on the technologies and processes involved, we should also talk about them from a different angle, one that we focused a lot lately: types of water filters defined by their installation/use method.

whole house - under sink - pitcher water filters

As we said, you should do some research on home water filter systems before you go purchase one, as you will find yourself looking at a broad category of water filters, each with its own tech specs, features, levels of efficiency, and installation requirements.

So let’s see the most common water filter systems depending on size, function, installation method, and maintenance needs.

1. Whole House Water Filters

The best whole house water filters are capable of providing you around 100,000 gallons or more of clean, soft, safe water until you need to replace the filter(s). Here are the main things you should know about:

  • Large and heavy devices, usually installed in large homes or office buildings/businesses.
  • They use absorption or reverse osmosis (with or without UV filters to boot) water purification technology.
  • They are expensive.
  • Most of them require a professional plumber and tools for installation.
  • Make sure you know when and how to change the filters.
  • Some of them also soften the water, some work best with an added water softener.

2. Under Sink Water Filters

Smaller than their whole house counterparts but efficient in their own way, some the best under sink water filters can provide you with about 3000 gallons or more of mineralized water on tap! Now let’s discuss the under sink water filters that we have talked about a few times before!

  • Medium-sized devices requiring enough space to fit under your kitchen or bathroom sink.
  • Most of them use reverse osmosis as a means to purify drinking water and mineralize & alkalize it for better taste and health benefits.
  • They are medium-priced and some are incredibly affordable for their tech specs.
  • Not all of them require professional plumbing skills.
  • You should also pay attention to when and how you should change the filters for maximum efficiency.
  • They work well with water softeners.

3. Faucet Water Filters

Faucet water filters are convenient in many ways: small, easy to install, and ready to turn your tap water into something to enjoy, encouraging you to drink more water daily and finally break up for good with plastic water bottles. Let’s recap some of their best features!

  • Small, compact, and lightweight, most of them work with standard faucets.
  • Some of the best faucet water filters can provide you with around 320 and more gallons of clean, safe tap water every time you reach for the faucet.
  • They remove the most common water contaminants in drinking water.
  • Their price is affordable.
  • You do not need special pro plumbing skills to install them, although you can ask for instructions.
  • Some of them have an incredible environmental value.

4. Countertop Water Filters

When you rent or travel/move a lot, you do not want to invest in massive equipment, hi-tech devices, or things you couldn’t possibly carry with you to your next place of residence. In such situations, countertop water filters may be the answers to all your problems.

They come in many forms and functions, but we will discuss three main categories of water filters you can carry around and display in your kitchen without them taking too much space.

4.1. Water Pitchers and Dispensers

The best water filter pitcher you buy should purify and sanitize your water, save you a handful of plastic water bottles, look nice on the countertop, and filter enough water a day for you to really enjoy the full health benefits of drinking water. Here is what you should know about water filter pitchers and dispensers:

  • Some water filter pitchers use multi-stage filtration to balance your water’s pH and clean it of impurities.
  • Most of them look amazing and make excellent portable kitchen accessories, no matter where you go.
  • The price is more than affordable, even in the “expensive” department.
  • Make sure you find replacement filters for the brands you want to try.
  • Make sure you know when and how to change the filters, although many pro water filter pitchers come with notification systems.
  • The filtration time/cup of water is very important, so you should factor in this feature in your purchase decision as well.

4.2. Water Coolers with Incorporated Filter

Water coolers have a specific purpose to provide you with cold, room temp, and hot water whenever you want. Granted, some of the best water coolers are bulky devices placed in homes, offices, or businesses, but you can find countertop water coolers with incorporated filters as well.

  • The best water cooler with filter models usually relies on the absorption technology/process, as they come with activated carbon filters.

5. Portable Water Filters

While water filter pitchers are portable (and, to some extent, under sink water filters as well), in this category we find mostly two types of water filters:

5.1. Filtered Water Bottles

Filtered water bottles are the answer to dynamic and active peoples’ prayers regarding the elimination of plastic single-use water bottles. A water bottle with filter usually uses absorption technology – carbon filters – to turn the most contaminated of waters into clean, safe drinks. Here are some things you should know about:

  • Some of the best filtered water bottles are capable of removing the usual suspects you find in mountain stream water and also more dangerous contaminants (heavy metals, inorganic, industrial, and even radiological contaminants.
  • You should pick your best filtered water bottle depending on your needs – some fit best the urban active professional, while others have adventurers, extreme sports buffs, and survivalists in mind.
  • One single filtered water bottle can replace up to 600 plastic water bottles a year while also being recyclable, so you don’t get any eco-friendlier than this.
  • As the price goes, some may be a bit expensive to carry around in a purse or a backpack to and from the office, but some feature excellent price/value ratios if you intend to spend a week in the harshest wilderness.
  • Look for the filter life feature on each filtered water bottle that sparked your interest. The higher, the better. Not to mention you have to know how much money you spend by getting replacement filters.
  • You can use them at home as well together or instead of your water filter pitcher.

5.2. On the Go – RV Water Filters

When you travel a lot in your RV and camp a lot, you need clean safe water no matter where your wanderlust takes you. If you search carefully, you will find compact on-the-go whole house water filters for RVs.

How do Water Filters Work: The Essential Tech Specs

water filters under sink remove contaminants

We have listed the essential tech specs for each type of water filter we reviewed, but we feel that it is important to recap the most crucial of them if we want to know how water filters work.

  • Filter life – measured in months and/or gallons, they indicate how much filtered water you enjoy before you have to change the filter.
  • Technology/process – make sure you choose what is right for you and your family, the business, or office team. If your water is just hard and having a funny smell/taste, you may want to go for a water softener or a faucet water filter. If the water you use daily comes from a well or features high levels of contamination (even in the city), you may want to look for whole house water filters or under sink water filters based on absorption or reverse osmosis.
  • Maintenance – this is an important aspect that not many people consider. Make sure any type of water filter you buy, you will find good customer service, affordable replacements (the filters are usually the main concern here), reliable warranties from the manufacturer, and so on.
  • Ecological impact – while it is true that reverse osmosis water filters do waste some water, you can reuse it for the house/business with no problems. Other than that, using any type of water filter system should allow you to give up plastic water bottles and jugs, protect your plumbing and your appliances, and make the world a better place.

Before we depart today and as a part of our guide on how do water filters work, we want to offer you this compact guide on how to pick the right water filtration system depending on the type of water issues you may encounter.

Matching the Problem with its Solution

Situation Solution
Contaminated city/well water (big house/family) Whole house water filters with absorption/reverse osmosis
Contaminated city/well water (medium/small house or family) Under sink water filter with reverse osmosis
Hard water/stains on dishes/dry skin/funny water smell A water softener
Really bad taste and odor on tap water Faucet water filters or RO water filters
Medium bad taste and odor on tap water Water filter pitchers
Bacteria/viruses/microorganisms in the water RO whole house water filters/under sink water filters & mandatory additional UV filter
RV travel and living On the go whole house water filters for RVs
Moving around, renting, changing destinations often Faucet water filters or water filter pitchers
Contaminated water outdoors Water filter bottles


We hope you enjoyed our guideline on how do water filters work and how you should understand their tech specs, features, capabilities, and limitations. If you do use a water filter – of any kind – feel free to share with us your opinions about it! Does it work as you expected? Did it help you enjoy clean and fresh water, eliminating plastic water bottles from your everyday life? Leave us a comment below!

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