Overview of water filter technologies
Filtering drinking water at home can reduce contaminants that water utilities don't remove. It can also help with reducing contaminants from water utility treatment, such as disinfection byproducts, and from the water distribution system, such as lead.
Most water filter products on the market use one or a combination of two primary technologies: carbon filtration and reverse osmosis.
Common Filter Technologies
Carbon-based
The majority of commercial carbon filters use activated carbon. This traps and removes contaminants as water flows through the filter. These filters consist of high carbon materials, like coconut shells or wood, that have been heated to create a porous structure.
The effectiveness of these filters can vary significantly.
Some are certified only to reduce chlorine from water treatment, improving taste and odor. Others can reduce the levels of contaminants such as lead, disinfection by-products and volatile organic compounds, or VOCs.
Activated carbon filters are less effective at removing some contaminants, such as nitrate, perchlorate and 1,4 dioxane.
Carbon filters are typically sold as either carbon block or granulated activated carbon.
Carbon block filters contain activated carbon that is shaped into dense blocks under high pressure. They’re usually more expensive than granular activated carbon but are generally more effective in removing a broader range of chemicals. That’s because they have more surface area that comes into contact with water and a slower rate of filtration. But they may need to be replaced more often.
Granulated activated carbon filters contain loose, fine grains of activated carbon. They are usually somewhat less effective than carbon block filters, because the water flows through them more quickly.
Reverse osmosis
Reverse osmosis systems sold for home installation typically also include one or more activated carbon and sediment filters, which reduces or removes a large range of contaminants.
The initial activated carbon treatment captures and removes chlorine, trihalomethanes and VOCs.
Next, during reverse osmosis filtration, tap water is pushed under pressure through a semipermeable membrane that blocks any particles or contaminants larger than water molecules. As a result, reverse osmosis systems effectively remove a wide range of contaminants, like arsenic, hexavalent chromium, nitrates and perchlorate.
The primary drawback of reverse osmosis systems is how much water they waste. These systems require inputs of about three to five times more water than they produce, and the extra water flows down the drain.
Reverse osmosis filters also remove minerals that improve the taste of water and are essential for health, such as iron, calcium and magnesium. Some manufacturers of reverse osmosis systems may offer options to address this problem, like mineral drops consumers can add back to their water.
Other kinds of filters
Ion exchange and water softeners
Water softeners typically use an ion exchange process to reduce levels of calcium and magnesium, which can build up in plumbing and fixtures, as well as barium and radium, which can be found in treated tap water. The levels of other contaminants usually remain unchanged.
Since water softeners replace calcium and magnesium with sodium, doctors may advise people with certain health conditions, such as those who wish to maintain a low-sodium diet, to avoid softened water.
This type of filtered water is also not recommended for watering plants and gardens, since salty water can harm plants.
Distillation
This technology heats water enough to vaporize it and then condenses the steam to form water again.
The process removes minerals, many bacteria and viruses, and some chemicals that have a higher boiling point than water. But it may only partially remove chlorine, trihalomethanes or VOCs.
Home distillation systems are less common than other types of water filters.
Whole house filters
Whole house filters are installed at the point where water enters a house, so that all taps and appliances receive filtered water. These systems can use ion exchange, reverse osmosis or activated carbon technology.
This type of system is expensive compared to point-of-use filtration and is usually not necessary in most cases. An example of when a whole system might be needed is if the water contains high levels of radiologicals or high levels of iron that may damage home appliances.
Since whole house systems can remove chlorine, they may introduce the additional risk of harmful bacterial growth in plumbing.
Whole house reverse osmosis filtration systems waste a large amount of water.
February 2025