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Back when I started working in water filtration, I thought I had a basic understanding of how water filters worked. After about 6 months, I realized how little I actually knew. Even now, I’m still learning and trying to keep up with the research and breakthroughs in the field.

Luckily, I have a background in education so I think I can summarize my years of learning into something that should take a couple of minutes to read. Hopefully, by the end of this, you’ll have a better understanding of: 

  • how water filters work and 
  • why stronger filtration isn’t always better.

Let’s get into it.

First, water filtration is a spectrum, from easy and mild to hard and perfect

 Easy filtration results in mild changes to the water. Easy filtration is passive. You pour the water into a simple plastic pitcher, gravity pushes the water through that thing, and the water on the other side has been changed in some way. Like pouring a pot of pasta through a strainer.

Hard filtration results in perfect water. Hard filtration is active. Water is shoved against something, pressing so hard that only pure water comes through. The water is so pure at this point, it needs minerals added back in to be safe for human consumption.

Easy filtration is what you find in pitcher and countertop filters. Hard filtration is what you find in reverse osmosis systems. 

Somewhere in the middle of the spectrum is where undersink water filters fit. Undersink water filters are designed to be installed directly beneath a kitchen sink. The most common undersink water filters use a combination of filtration and adsorption (that’s aDsorption, with a D).

To clarify, aDsorption is when things stick to the surface of something. And aBsorption is when things stick to the inside of something. 

Here’s an example: any time you see ‘activated carbon’, think “fluffy charcoal”. Charcoal has been used to filter water since 400 BC. In the early 1800s, we figured out how to increase the number of tiny holes in charcoal’s surface, ‘activating’ it and making it more efficient. This allows it to aDsorb stuff.

What makes an undersink filter good

Many undersink water filters use activated carbon as the primary filtration medium. Since undersink filters are directly attached to the plumbing system, the pressure pushes the water against the activated carbon. So, not passive and therefore not easy filtration.

The good undersink filters have pre-filters or sediment filters designed to remove larger particles, debris, and sediments from the water. This helps prevent clogging and extends the lifespan of the main filter. 

Others may include additional filtration media, such as catalytic carbon, KDF (Kinetic Degradation Fluxion), or other specialty media designed to target specific contaminants like heavy metals or bacteria.

The most complex undersink water filters are microfiltration or reverse osmosis (RO) systems. Like I mentioned earlier, reverse osmosis systems are hard filtration systems. So, they usually have a remineralization stage where they add salt and other minerals back into the water. 

So, knowing this, how can you tell if a water filter is right for you? Well, it depends on what you want.

How to choose a water filter

If you want the simplest, easiest water filter, you can use any pitcher or countertop filter that uses activated carbon. Sure, it won’t remove a lot of contaminants, but it will improve the taste and clarity of the water. And it’s cheap, simple to replace, and better than nothing.

If you live in an area like the Southwest with heavy metals like arsenic in your groundwater, you should not rely on easy filtration. You need hard filtration to get those heavy metals and other really ‘sticky’ contaminants out of your water.

If you’re not sure about your water quality, a simple water test will give you a starting point. Once you know that, you can select an undersink filter to address your specific situation. 

You want (oh god I’m so sorry for this) The Right Filter (see what I did there?)

Learn more on Undersink Filteration.