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Types of Water Filters

Are you considering filtering your tap water but aren’t sure about different types of water filters? Water filtration can be a tricky topic. Having some basic background information about the types of water filters for home and what to look for in a water filter can help clear up any confusion and provide you with purified water throughout your home.

While you might think of different types of water filters as similar, there are some significant differences that you should be aware of before you invest in a system. Understanding which contaminants a filtration system is effective against and which contaminants it isn’t effective against can help you find the system that is appropriate for filtering your tap water. 

An Introduction to Filtration

Before discussing the different types of water filtration systems available, it is helpful to first have a broad overview of filtration itself and why it is necessary. 

Water filters for residential use may use a combination of physical, chemical, or biological processes for reducing or removing contaminants from water entering a home. Residential water filters tend to use physical filtration media most often. What this means is water containing contaminants is run through a physical media that absorbs, traps, or stops the contaminants.

Contaminants in water can be liquids, gases, or dissolved and suspended solids. Not all filters are effective against all types of contaminants. While one type of filtration method may be highly effective against certain types of contaminants, such as protozoa or bacteria, it may not be as effective at removing chemicals. 

Put another way, each filtration method has advantages and disadvantages for removing certain types of contaminants. Because of this, many filtration systems utilize more than one filtration method within the same system. Sometimes these are referred to as multimedia hybrid systems, which is a reference to the multiple types of filtration media contained within the system itself.

Point-Of-Use vs. Point-Of-Entry

Which kind of filtration system you use will ultimately come down to how you plan on using your water filter, what you need it for, and other factors like your lifestyle, budget, and living situation. In a residential setting, there are two broad categories of filtration systems.

The first category is “point-of-use” (POU) systems. These water purification systems are installed where you are planning on using them. The easiest example is a system installed under a sink to provide filtered drinking water. The advantage of these types of house water filtration systems is that they have a smaller footprint and are typically less of an investment. The downside is that contaminants are only reduced on the line where the system is installed. So, while you’ll have fewer contaminants in your drinking water, the water you bathe or shower with will still contain a higher level of contaminants.

The second category is “point-of-entry” (POE) systems. POE systems are installed where municipal water enters your house, and are intended to filter all of the water throughout your house rather than at a single faucet. The advantage of these systems is that they reduce or remove contaminants everywhere in your house, including your showers and every sink. This can make a big difference, not only to lessen exposure to specific chemicals but also to increase the longevity and effectiveness of certain appliances if you are using a system that softens hard water.

The downside of POE systems is that they typically require more of an investment than a point-of-use system. Also, certain filtration methods like reverse osmosis tend to be used at the point-of-use, though Rayne does offer reverse osmosis water filter systems for your whole house, so it is always an option if you find that your use and circumstances require reverse osmosis filtered water at every tap in your home. If you’d like further information, view our guide to how to install water filters.

Common Filtration Methods

The two most common types of water purification methods are reverse osmosis and granulated activated carbon. It is also worth taking the time to understand water softening systems since these are sometimes used in conjunction with one or more of the other filtration methods to filter out a broad spectrum of contaminants. Let’s take a look at each of these house water filtration methods in greater detail.

Reverse Osmosis

If you are looking for residential water filtration options you will definitely run across reverse osmosis (RO) systems, so gaining a better understanding of how these systems work will help you determine if they are right for you.

As the name would imply, reverse osmosis water filter systems turn around the natural process of osmosis. In osmosis, a liquid naturally flows from a solution with a low concentration of solutes to a solution with a high concentration of solutes. This flow occurs across a semipermeable membrane, such as the cell wall of a plant’s roots or the cells in our body. Osmosis is how plants absorb water from the soil. Water flows from the soil which has a low nutrient density and into the plant which has a high nutrient density.

In terms of water treatment, reverse osmosis systems function by forcing water that contains contaminants through a specially constructed membrane with very small pores. Those pores only let water molecules and some very small contaminants through, while the majority of contaminants or unwanted particles are left behind and disposed of.

The easiest way to visualize reverse osmosis is by looking at desalination plants, which use reverse osmosis to remove salt from seawater. To desalinate water, salt water is forced through a membrane at high pressure. The membrane allows water molecules through but doesn’t allow salt through, so the end result is purified water.

Reverse osmosis is a powerful filtration method but like all filtration methods, it doesn’t remove all contaminants.

RO systems are effective at removing:

  • Nitrates
  • Salts
  • Heavy metals like lead, copper, iron
  • Protozoa (Giardia, Cryptosporidium, etc.)
  • Bacteria (Salmonella, Shigella, E. coli, etc.)
  • Viruses (Norovirus, Hepatitis A, Rotavirus, etc.)
  • Reduces arsenic, fluoride, sulfates, potassium, and phosphorus. 

RO systems are less effective at removing volatile organic compounds (VOCs), as well as chemical disinfectants that are used to treat water such as chlorine. Because of this, many RO systems integrate pre- and post-filters, often using activated carbon, which filters out many of the contaminants and particles not filtered by the reverse osmosis process itself.

Activated Carbon

Activated carbon is probably the most common type of media used in residential filtration systems. It may simply be referred to as activated carbon or granulated activated carbon (GAC). Activated carbon is a type of charcoal that has been treated with oxygen or heat. This treatment dramatically increases the surface area of the carbon. To get a sense of how large the surface area of this filtration media is, approximately 1 gram of activated carbon has a surface area of roughly 32,000 feet.

The vast surface area of activated carbon is important because it filters contaminants through a process known as adsorption. Adsorption is the process where a solid, in this case, carbon, traps molecules of a gas, liquid, or solute on its surface. As tap water flows through the activated carbon granules in the filter, contaminants are trapped on the surface of the carbon while the water continues to flow through. Eventually, activated carbon filters will need to be replaced as the available surface area for adsorption to occur diminishes.

Activated carbon is effective at removing the following contaminants from water:

  • Volatile organic compounds (VOCs)
  • Disinfectants used in water treatment like chlorine and bromine
  • Industrial solvents
  • Some pesticides.

While activated carbon is excellent at removing the chemicals and compounds that give tap water an unpleasant taste and odor, it is less effective at removing other contaminants. These include heavy metals and mineral ions that contribute to water hardness, nitrates, microbes, and fluoride which is often used in water treatment in the United States.

Water Softening Systems

Water softening systems are not usually lumped together with water filters, but it is worth spending a moment understanding exactly what these systems remove from your water.

Water softener systems remove the mineral ions that contribute to water hardness through a process known as ion exchange. As water flows through the system, mineral ions are attracted to resin beads in the system and replaced with sodium ions. 

Water softener systems remove minerals such as calcium and magnesium, as well as heavy metals such as lead, copper, or iron. They don’t remove other contaminants such as microbes, VOCs, pesticides, or solvents. Typically, water softening systems are point-of-entry systems that soften water for the whole house. Often they are combined with other point-of-use filtration systems, such as an RO system installed under a sink to provide safe drinking water.

Final Thoughts

The two most common types of filtration systems for residential use are systems using reverse osmosis or activated carbon filters. Both of these systems are effective at removing contaminants, but the exact type of contaminants they remove are different. Because of this, many filtration systems actually combine both filtration methods to offer a broad spectrum of contaminant removal.

For example, many RO systems have pre- and post-filters, at least one of which uses activated carbon, which helps the system remove contaminants not captured by reverse osmosis.

Determining which of the types of water filters is right for you can be difficult. We recommend starting with a test of your water supply so that you can have a firm understanding of exactly which contaminants you need to be concerned about. From there, you can narrow down the systems that will meet your needs — in terms of living style and cost of water filters. If you’re looking for information on price, visit our guide to How Much Do Water Filters Cost.

To learn more about water filter options or to schedule a home water test, please contact Rayne Water today.

Sources:

  1. https://www.cdc.gov/healthywater/drinking/home-water-treatment/household_water_treatment.html
  2. https://www.explainthatstuff.com/howwaterfilterswork.html
  3. https://science.howstuffworks.com/environmental/energy/question209.htm
  4. https://www.cdc.gov/healthywater/pdf/drinking/Household_Water_Treatment.pdf
  5. https://www.health.state.mn.us/communities/environment/hazardous/topics/gac.html#GACuse
  6. https://www.pca.state.mn.us/sites/default/files/c-s1-05.pdf