Whether you have a water filter in your water pitcher, on your faucet, or underneath your sink, you might wonder how water filters work. If you’ve heard of recent water contamination events, you might also wonder what contaminants your water filter actually removes. Let’s take a closer look at how water filters work and what they remove from your water.

Types of Water Filters

There are many different types of water filters. Water filters vary by the type of filters they use, and their construction. Each filter works a bit differently, though some of the basic principles are the same. These are a few of the different types of filters. Keep in mind that some of these filters overlap.

• Pitcher filter: Filters installed in water pitchers are very common. These filters need to be replaced regularly and filter water as you fill it.
• Faucet filter: Water filters attached to your faucet filter water as it runs through. The filter media also needs to be replaced at regular intervals to keep the water clean.
• Under-sink filter: These types of filters connect to the plumbing directly under your sink and filter water as it moves through the pipes.
• Carbon filter: These types of filters use activated carbon to filter water. Carbon filters are used in many of the filters previously mentioned.
• Ion exchange: Ion exchange filters are often used to soften “hard” water that contains excessive magnesium and calcium.
• Reverse osmosis: This type of filter uses pressure to force water through a semipermeable membrane or several membranes to catch contaminants and filter them out.

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How Do Water Filters Work?

As previously mentioned, different types of water filters work in slightly different ways. These different processes will remove different types of contaminants, which we’ll discuss in more detail later in the post. First, how do each of these filters work?

• Activated carbon: Carbon-based filters use the principle of adsorption (different from absorption) to capture a variety of contaminants. However, there are different types of carbon filters that remove different things.
• Micron filtration: Filters with very tightly woven material allow only very small particles to pass through. This type of filter captures even very small particles like bacteria, but won’t be able to capture fully-dissolved materials or extremely tiny particles, like viruses.
• Ion exchange: Ion exchange filters use small resin beads to remove “hardness” from water, usually excess minerals like magnesium and calcium. The resin beads naturally pull in these minerals through the principle of ion exchange.
• Reverse osmosis: This type of filter is highly effective. Using pressure, varying levels of concentration, and tightly-woven membranes, reverse osmosis filters pull contaminants out of the water. These filters generally use multiple layers of filter media, including semi-permeable membranes and carbon, to filter out different contaminants at different steps in the process.
• Sanitation: Ultraviolet light, ozone, and chlorine can all be used to sanitize water. Though these are not technically types of filtration, these processes are essential to kill bacteria and viruses, and make water safe to drink.

What Do These Water Filters Remove?

There are many contaminants that water filters might remove. Different filters are able to filter different things, so it’s important to reach the labels carefully if you are looking for a filter that removes certain contaminants. Here are a few things that many consumers are concerned about filtering from their water:

• Sediment: Many filters are capable of removing things like dirt and grit. This is also an important part of any water purification process. Your municipal water system or your home well system should remove these particles. If you’re finding dirt or grit in your water, there may be a problem with your water system or you may have a water advisory notice active in your area.
• Parasites: Parasites are very small organisms that live in most wild water sources, from ponds to oceans. Removing parasites is one of the reasons it is essential to treat water before consuming it. Most water filters will remove parasites, since these organisms are generally too large to pass through the filter media. However, if you’re consuming untreated water or you aren’t sure about the source, you should boil the water before consuming it.
• Bacteria: Not all bacteria are bad, but some types live in water and can make us very sick. Many water filters are designed to filter out bacteria. Bacteria sometimes live in a substance called biofilm, which can accumulate in pipes or faucets, and cause an unpleasant odor, while also making the water unsafe to drink. If water is contaminated with wastewater, bacteria can also become a serious problem.
• Viruses: Viruses are about 10 to 100 times smaller than bacteria and most filters cannot remove them. To remove viruses, it’s important to sanitize the water by boiling, chlorination, UV sanitation, reverse osmosis, or another method. Just like bacteria, biofilm or wastewater contamination can cause viruses to become a serious problem.
• Chemicals: Similar to bacteria, not all chemicals are bad. Chlorine, for example, is often used in municipal water treatment to destroy harmful pathogens. In the right amounts, chlorine can keep water safe. But, if there’s too much chlorine in the water, it can be a problem. This is true for many different types of chemicals. Some chemicals, like lead, are harmful in very small amounts and there is no safe level of consumption. Copper, for example, can be harmful in larger amounts, but small amounts are normal and safe. Potentially harmful chemicals can get into the water supply in many different ways, from fertilizers and pesticides on crops to industrial coolant and industrial waste to old pipes and plumbing and more.

Completely removing all other compounds or microorganisms from water and leaving only pure H20 is extremely difficult, but it’s also not necessary to have healthy water. It’s important to filter out the things that can make us sick or things that can make the water taste or smell bad. The NSF water filter rating system can help you determine which filters will remove which contaminants. Read the labels of each filter carefully before choosing which is right for your home.