Tech Check

Updated on:
November 13, 2023

One of the first things we do in our water filter review process is examine the filter technology used in a given product. 

As you probably already know, there are lots of different ways to filter water. Before we consider recommending a product, we first verify the manufacturer is using appropriate technology. 

We also want to make sure it’s not trying to pass snake oil off as the “newest and best thing.” This isn’t totally uncommon to see, but we are always on the lookout for false claims. 

To give you an idea of why this analysis is important, here are some of the most common and effective filtration technologies available today:

Sediment/Particle Filters

The primary function of sediment/particle filters is to remove suspended solids from a water supply, such as dirt, sand, silt, clay, etc. 

They are usually made of some sort of synthetic material, typically plastic, such as polypropylene. 

The biggest difference from one sediment filter to the next is the micron rating. A micron is a unit of measurement also known as a micrometer. It’s one millionth of a meter, or .000001 meters. In the imperial system, this is 1/25,6000 of an inch. 

The micron rating of a sediment filter refers to the size of the pores in the filter. It can remove any particle larger than its micron rating. Anything smaller can still get through. 

For sediment filters, 5 microns is a common rating. Most dirt, sand, silt, etc. is going to be larger than this. To give you an idea, anything lower than 40 microns is invisible to us unless we have a microscope. 

Some filters go even further and have ratings of 1 micron or even 0.5 microns. The purpose of this is to try and catch additional contaminants. But the danger is that these ultrafine filters can get clogged more easily since they catch more stuff. This can cause a drop in water pressure. 

Sediment filters are sometimes also called cartridge or canister filters due to how they are designed. They are stored inside a filter housing that looks like a cartridge or canister. They typically need to be replaced every six to nine months because they will fill up with sediment. This may be required sooner if there is a lot of sediment in your water. 

Sediment filters are most commonly used for well water. Runoff and loose well caps can cause all sorts of dirt and dust to get into your water supply, and a good sediment filter will remove this before it gets to your tap. 

They are often included in larger filtration systems as pre- or post-filters. Pre-filters remove sediment before the water gets to another part of the system, such as a water softener, to help improve the efficacy of these other devices, as well as prolonging their lifespans.

If it’s included as a post-filter, it’s the last stop your water makes before moving to the tap to remove any large particles missed by the rest of the filtration system.

Many water filters come with a sediment filter included as part of the system. But many do not. 

When we look at a product, we check to see if one is needed. Often a warranty may no longer be valid if you don’t properly pre-filter the water before it runs through the rest of your system, and this is not always clear. 

If one is included, we check to make sure it’s designed correctly and it’s going to add value to the overall system.

We also verify that the manufacturer is not misrepresenting what the filter can do. Most bacteria and viruses are between 1 and 2 microns. So, a 5-micron filter will not be effective against these contaminants. 

We take all of this and more into consideration when reviewing a product. 

Activated Carbon

When you look at water filters, you will no doubt come across the term “activated carbon.” It is sometimes referred to as “granular activated carbon,” or GAC. 

Activated carbon is a filter technology that comes from taking a substance high in carbon (coconut husks or coal are good examples) and heating it without the use of oxygen to expand its surface area. Think of cooking popcorn over the stove. The heat causes the kernels to expand, given you more surface area for the salt and butter. 

A similar process takes place during the carbon activation process.

Activated carbon is such a popular material because it is porous and adsorbent (which is not the same as absorbent).

Since it’s porous, it allows water to pass through it. But as the water goes through, certain chemicals are attracted on a molecular level to the carbon, causing them to stick to it. This removes them from the water supply. 

Activated carbon is most effective against chlorine, chloramine, volatile organic compounds (VOCs), per- and polyfluorinated substances (PFAs), many pesticides, and benzene. It’s also effective against hydrogen sulfide in lower concentrations, which means it can help remove that rotten egg smell from your water. 

Because of its effectiveness against these chemicals, activated carbon is an effective filter for city water. Municipal water is allowed to have certain levels of these contaminants. This means the water is safe, but it can have significant impacts on its taste and smell.

Activated carbon can be used in well applications, but only if these chemicals are in your water. If you have iron or nitrate (relatively common in well water), activated carbon will not be effective.

One important thing to keep in mind with activated carbon is that it does have a limited lifespan. Over time, as chemicals bind to the surface, there will be no more “room” for the contaminants and the filter ceases to function. At this point, you need to replace the filter. 

In addition to verifying manufacturer claims about activated carbon, we also look closely at filter life and the cost of replacements.

KDF Media

When looking into water filters, you will undoubtedly come across the term KDF media. 

KDF stands for kinetic degradation fluxion and is a mixture of high-purity copper and zinc that removes a number of contaminants from water.

Using a number of different chemical processes, KDF media is able to remove chlorine, chloramine, hydrogen sulfide, iron, copper, lead, nickel, and mercury from your water supply.

KDF media also has a mitigating effect against microorganisms, such as bacteria, fungi, and algae. It should not be used as primary defense against microbial contamination, but it can be used alongside other filter technologies to protect them and extend their life. 

For example, KDF is often used in conjunction with activated carbon. The KDF media will remove chlorine and chloramine, leaving more space on the activated-carbon granules for other contaminants. It will also prevent microbial growth on the activated carbon itself, which helps extend its life and makes it more effective in the long run. 

While highly effective against a number of contaminants, KDF is often best used in conjunction with other filter technologies since it is not effective at removing organic compounds (VOCs, PFAs, benzene, pesticides, etc.). It is also not effective against microbial contamination from viruses and bacteria. 

KDF media can be used for both well and city water so long as it’s combined properly with other filters to tackle the contaminants it cannot remove from the water supply.

Manufacturers often include the words “KDF media” in their descriptions of products but don’t always explain exactly how it’s integrated into the system. 

When we look at a product, we check to see exactly how KDF is used so that we can verify its effectiveness, determine the right use for the product, and make an appropriate recommendation.

Air Induction Oxidation

Many contaminants are unrecognizable to us until the water gets to the faucet. This is because when water comes into contact with the air, contaminants go through a process of oxidation. 

A perfect example of this is what happens when hydrogen sulfide (often referred to just as sulfur) is in your water. As the water comes out of your faucet and touches the air, the hydrogen sulfide oxidizes and causes your water to smell like rotten eggs.

Iron and manganese are similar to hydrogen sulfide in that they react to the oxygen in the air. But instead of making your water smell, they leave behind ugly stains on your sinks, showers, tubs, etc. 

Many of the filters designed to tackle these contaminants use a process called air induction oxidation or air injection oxidation (AIO).

What this does is force your water supply into contact with air before it reaches your faucet. It usually does this inside the filter housing by spraying the water over a pocket of compressed air when it enters the filter. The water is then passed through a filter media to catch the newly oxidized compounds. 

When the water gets to your faucet, these compounds have been removed and so have their negative effects on your water. 

Since AIO is specifically designed for removing sulfur, iron, and manganese, it is primarily a well filter solution. 

Whenever a product we’re reviewing features AIO technology, we take a look at a few things. 

First, we want to see how the air pocket is created. Older technologies, or those designed for heavy-duty commercial use, employ an air pump to add more air to the system and increase filtration capacity. Most units today use a venturi, which sucks air into the pocket and is silent. 

We also take a look at the filter media being used to catch the oxidized particles to make sure it can handle the job of removing these contaminants. 

If we recommend a product using AIO, you can be sure we’ve vetted it and can verify its performance capabilities.

Reverse Osmosis

Reverse osmosis (RO) is another very common filtration technology that has a lot of benefits but also some significant drawbacks. 

As the name suggests, it works by reversing the natural flow of water that occurs during osmosis. 

In regular osmosis, water separated by a semipermeable membrane will naturally flow to equalize the levels of solutes present on both sides of the membrane. It will move through the membrane from the low-solute solution to the high-solute solution until equilibrium is achieved. These solutes cannot pass through the membrane, but the water can. 

In reverse osmosis, pressure is used to force water in the opposite direction. It will travel from a high concentration to a low concentration, passing through a membrane that filters out contaminants. 

When this happens, clean water is “produced” and stored in a tank. It will then travel to your faucet when there is demand. The remaining solution is then flushed down the drain. 

This makes reverse osmosis systems inherently wasteful, which is one of the things we look at when evaluating RO systems. RO efficiency is measured in a ratio of wasted to produced water.

The semipermeable membranes used in RO systems have very small pores, usually 0.005 microns, which allows them to catch heavy metals, such as lead and copper, as well as viruses and bacteria. It’s the most effective filtration technology against water with high concentrations of salt, making it an excellent option for those living in coastal areas with high water salinity. 

Because of its effectiveness against a wide range of contaminants, RO can be used on both city and well water supplies. However, it is not effective against chlorine, chloramine, VOCs, PFAs, and other common city water contaminants, so it would need to be paired with something else to be truly effective in this application.

Efficiency ratings are important when evaluating RO systems. We also look at daily production capacity and storage tank sizes. Many RO systems also come with pressure pumps to make sure there’s enough pressure in the system at all times. 

Pre-filtration is also an important component of an RO system. Because of its super small pores, RO membranes are easily clogged and damaged. For example, it’s highly recommended to soften your water before running it through an RO system to prevent scale buildup that can reduce the effectiveness of your RO system.

Reverse osmosis systems tend to be more expensive than other options, so before we recommend a product, we do a deep dive into all the variables that can impact its effectiveness. This ensures the solution we offer is going to truly meet your needs.

UV Purification

The use of ultraviolet light in water filtration is a highly effective way of removing microbial contaminants such as bacteria, protozoa, and viruses. 

The technology is fairly simple: Water goes into a chamber where it is exposed to a high dose of UV light. The UV light penetrates these contaminants on a cellular level and alters their DNA, rendering them incapable of reproducing. This effectively kills them and makes them completely harmless if ingested. 

However, effective UV purification can be a bit finicky. For example, unless you have impeccable water quality, pre-filtration is almost required. The presence of sediment or other large contaminants can cast shadows in your water and prevent the UV light from reaching all the microbes. 

In fact, many UV purifier manufacturers void their warranties if your water doesn’t meet certain standards before entering the UV chamber. 

UV purifiers also come with some more delicate technology, such as the lamps themselves, which need to be replaced more often. For example, all UV lamps are designed to last one year. But some options, such as LED UV lights, can last longer. Electronic heads and ballasts which control the system are also prone to damage just like any other electrical product. 

Microbial contamination is extremely uncommon in city water because it’s disinfected at the treatment facility. It also shouldn’t be present in your well unless you have a broken or leaky well cap. For this reason, UV purifiers are often installed as an emergency filter and can be used for both city and well water supplies.

When looking at products to recommend, these are the things we take into account to ensure that you’re getting an effective product with a reasonable cost of ownership.

Ion Exchange and Salt-Free Conditioning

Water softeners are very popular “filters” that target calcium and magnesium, also known as “hardness” minerals. 

Hard water is water with a high concentration of these minerals. It can cause scale buildup on your appliances and fixtures, which looks bad and can also cause damage. It also prevents soap from lathering, meaning you need to use more to clean effectively. Hard water also leaves streaks and stains on glassware and can irritate sensitive skin and hair. 

A water softener will “filter” out these minerals and make your water soft, though this type of filter is almost never called a filter. 

Both well and city water can be hard, so these products can be used for either. 

Water softeners vs. conditioners

A big thing to look for is whether a product is a softener or a conditioner. Many manufacturers label their products as “salt-free softeners,” but these are really conditioners. They do not remove hardness minerals but instead convert them into crystals that minimize the effects of hard water, mainly scale buildup. You’ll still get streaks and stains, and you’ll still need to use more soap. 

Traditional softeners use a resin to trap hardness minerals and exchange them for sodium. The resin is then flushed with a brine solution (salt and water) to restore its capacity in a process known as regeneration. 

When reviewing hard water solutions, we look for things such as grain capacity, which indicates how much of these hardness minerals the softener can remove. We also look closely at maintenance costs. We try to estimate how often salts will need to be replaced, as well as how much water will be lost during the regeneration cycle. Many of the top options use smart features to better monitor the system and reduce waste. 

Given how much variation there is across water softeners, we spend a great deal of time comparing features and specifications to ensure you’re getting a product that will do what you need.

New Filter Technologies

Today, we know a lot about water filtration and have developed effective filter technologies to make clean drinking water possible pretty much everywhere. 

However, that doesn’t mean there is no innovation in this industry. It’s not uncommon to come across products with new, unproven technology that the manufacturer claims to be better and more effective for one reason or another.

When this happens, we get to work. Thankfully, there is a robust scientific community focused on water filtration that regularly publishes peer-reviewed content that can speak to the validity of a new technology. As industry experts, we know which publications can be trusted. 

If needed, we can try to test these technologies ourselves. But no matter what, before we recommend a product, we independently verify that the design is legitimate and can deliver on the claims being made by the manufacturer. 

All too often, though, we cannot do this. In the event a manufacturer is using an unproven or unnecessary technology to try and sell you their product, we immediately remove their products from our lists.

Reviews You Can Count On

As part of our rigorous product research and testing methodology, we look at every aspect of buying and owning a water filtration system. Product warranty is just one of many important factors we consider as we create product reviews you can count on.