How To Choose a Water Filter: What Kind of Filter Do I Need?

Wondering what type of water filter is best for your home?

You’ve come to the right place.

In this 15-minute post, I’ll explain the different types of residential water filtration technologies available, how they work, what contaminants they remove and their pros and cons.

This post is for anyone who is concerned about the quality of their tap water but doesn't know what kind of water filter they should buy:

• should you buy a whole house water filter?
• should you get an undercounter filter for drinking water?
• what about a reverse osmosis system?
• or do you just need a $20 faucet filter?

This guide to the different kinds of water filter technologies & types of water filters will help you answer this important question - in 5 minutes or less.

What's In This Guide

Water Filtration Technologies Explained

Even thousands of years ago, people knew that it was a good idea to purify water before drinking it.

Boiling water was a common method of purification. They also used gravel and sand to filter out sediment from water.

Then, people were mostly concerned about water turbidity – cloudiness caused by suspended particles like dust and silt.

They did not yet know about microscopic bugs like bacteria that were much worse than a bit of sand in the water.

We obviously know better today and we’ve invented a dozen new filtration methods to make sure water is actually clean and not just clear.

Modern filtration technologies work through different methods.

Some filter out impurities from water, only allowing water molecules to pass through the media.

Some use chemical process such as chlorination while others make use of electromagnetic radiation – specifically UV light – to purify water.

Here are the most common water filtration technologies used in home water filters.

Activated Carbon

Activated carbon in block and powder form. Source: Wikimedia​ 

This is the most common type of filtration media used in home water filters.

Activated carbon is charcoal that has been processed, using either hot gasses or chemicals, to increase its porosity.

It has a huge number of micro-pores that increase its surface area and which adsorb impurities in water.

When water goes through activated carbon, molecules of chemicals, small sediment particles and other impurities become trapped in the tiny pores within the internal surface area.

The carbon also reacts with chlorine in water to form chloride ions. This eliminates the unpleasant taste of chlorine and chloramines used in municipal water treatment.

What can Activated Carbon Remove?

What Can’t Activated Carbon Remove? 

Reverse Osmosis water filter

If you remember half of your high school biology, you may know a bit about osmosis.

It’s a process where water moves from a less concentrated solution through a semi-permeable membrane into a more concentrated solution.

Plant roots use it to absorb water from the ground and our kidneys use it to absorb water from the blood stream.

Reverse osmosis is the opposite. Water moves from a more concentrated solution to a less concentrated one.

But unlike normal osmosis, reverse osmosis cannot happen on its own. Pressure is needed to push water back through the semi-permeable membrane.

The membrane only allows water through. 99% of impurities are left behind.

Here’s a gif showing how it works.

That’s how a reverse osmosis (RO) filter works.

It is highly effective at ridding water of a wide range of chemicals, dissolved solids and harmful microbes.

What can a Reverse Osmosis Filter Remove? 

Note: Most RO systems consist of multiple filters.So in reality, the RO membrane in your filter may never come into contact with the chlorine in your water (which can actually damage it) since it has already been removed by a carbon pre-filter.

What can’t a Reverse Osmosis Filter Remove? 

Ion Exchange

Ion exchange is a physical-chemical reaction where an exchange of ions between contaminants in water and a resin bed is used to purify water.

An ion exchange filter works by passing water through bead-like materials called resins. As the water passes through, contaminants exchange their ions with the ions on the beads.

Ion exchange removes many dissolved solids in water including hardness minerals, toxic heavy metals and other dissolved inorganics.

Like most other filters, an ion exchange resin bed has a finite lifespan after which it needs to be replaced.

What can an Ion Exchange Filter Remove? 

What can’t an Ion Exchange Filter Remove? 

Because of these limitations, ion exchange systems usually consists of multiple-stages with several filters to remove different kinds of contaminants.

UV Water Filters

Ultra violet radiation is an extremely effective way of disinfecting water. UV filters specifically target microbes like bacteria, viruses and cysts, neutralizing over 99% of them.

UV disinfection works by radiating the cells of these microbes. This damages their DNA, preventing reproduction.

UV filters are easy to install, last a long time before you need to replace the bulb and consume very little energy.

But because they can only target microbes, you should only use it to complement other filters that can remove the other contaminants.

What can a UV Filter Remove?

What can’t a UV Filter Remove? 

Other Filtration Technologies

The above are the most common. Here are a few others you may not have heard about, including some advanced modern technologies.

Ceramic filters: Like activated carbon and RO membranes, ceramic filters also use a physical process to filter out contaminants. As water passes through the tiny pores in the ceramic, contaminants that can’t fit through are filtered out.

Ceramic filters can remove some microbes and sediment. On their own, they are not very effective at removing viruses (too small), chemicals and dissolved solids.

That’s why they are often combined with other types of filters, usually an activated carbon filter.

Activated alumina: This is a filtration media made from aluminum hydroxide. It is processed to create a highly porous material that works the same way as activated carbon.

Activated alumina is often used to filter out fluoride, selenium and arsenic from water.

Like activated carbon, activated alumina cannot remove microbes from the water. So it is necessary to combine it with a UV or RO filter to get pure drinking water.

Hollow fiber filters: Another filter that utilizes the size exclusion technique to remove contaminants from water. In this case, tiny pores in the fibers only allow water to pass through, leaving microbes trapped within the fibres.

Types of Water Filters Explained

Most of the filtration technologies/media we have discussed above are not used on their own. They are combined with other filters to create a multi-stage system.

This has a couple of benefits:

Whole House Water Filters 

A whole-house water filter treats all the water coming into your house. You install it on the main line into your house just after the water meter and before the heater.

It’s a good choice when you want all faucets and showers to produce treated water.

A whole-house filter typically has at least three stages though some systems can have as many as five or six.

The stages include a sediment pre-filter, an activated carbon filter and a post-filter.

Some systems also include a UV filter to neutralize microbes. Systems designed for use with well water have stages to handle dissolved solids like iron and manganese.

Under Sink Water Filters

If you only need filtered water for drinking or cooking, an under-sink water filter is a much more convenient and cheaper alternative to a whole-house system.

It goes under the sink – obviously – and connects either to the existing faucet or to a dedicated one.

Under-sink filters have at least 2-3 stages but some can have as many as six or more.

The stages includes sediment pre-filter and an activated carbon block.

RO under-sink filters also have an RO membrane plus an alkalization stage to reduce the acidity of filtered water. Most also pass the water through a mineralization stage to return stripped minerals.

Countertop Water Filters 

Instead of going under the sink, these filters sit on your kitchen countertop.

You connect a countertop filter directly to the end of your faucet and the filtered water comes out of a different faucet integrated into the filter housing.

They work essentially the same way as under-sink filters except that they are smaller, easier to install and connect to the faucet instead of the water line.

Water Filter Pitchers & Carafe Filters 

Under-sink and countertop filters are good and all but they are not very helpful when you are away from home.

If you want a portable solution, carafe filters are great.

This setup consists of a pitcher with an integrated filter. It can be a single type of filter, usually activated carbon, or a combination of 2 or 3 filters.

When you pour water into the pitcher, it passes through the filtration media. When you pour yourself a glass of water from the pitcher, it is free of chlorine, lead, sediment and a variety of other impurities.

Carafe filters are great for RVs, camping or for those who don’t want to go through the hassle of installing an under-sink or whole-house system.

What Kind of Water Filter Should You Buy? 

The answer is - it totally depends on your budget and needs:

If you are looking for a low-cost filter for a mid-size or large family, then buy an under-sink or countertop filter.

If you live on hard water or well water, then a whole-house water filter with a water softener option will protect your plumbing, clothes and appliances from the effects of dissolved minerals.

If you are looking for a filter for your RV or boat, then buy a countertop or carafe filter.

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