How does a home water filter work?

Have you ever wondered just how those neat little water filters actually work? How do they take dirty or impure water and clean it up so easily and quickly? Well, there isn’t a single answer to this as the different models of filter can work in different ways. A charcoal-cartridge in a jug doesn’t do the same thing as an under sink water filter.

Mechanical Filter

We can start with the most basic kind of filter, the “mechanical” type that is just a mesh that strains out your water. Most systems don’t rely on just this but it can be a first-stage unit in larger systems. Mesh can remove rust, sediment and sometimes larger microbes. Dissolved minerals and chemicals aren’t not removed.

Charcoal or Carbon Filters

You find these in the usual jug filters, and larger systems can often include a carbon-based unit as well. One of the biggest reasons why people have home water filtration is to deal with the taste of chlorine in the water, and that is what charcoal does best. The carbon has millions of tiny holes in it, and it works like a chemical sponge to absorb certain substances in your water.

It’s not quite the same as a plain mechanical mesh filter and not all substances will bond to the carbon. That means it will only filter out certain substances. Chlorine is the main one but it will also remove some organic compounds found in pesticides and herbicides too.

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Ion Exchange

We’re getting into more complex filtration technologies now, so it can be a little tougher to understand the principles behind them. An ion exchange system pulls contaminants out of the water based on electrical charge, swapping molecules for a harmless substance. Typically, these units are used for removing dissolved minerals in hard water using sodium to remove the calcium.

Reverse Osmosis

This is the ultimate in filtration techniques, and should remove nearly every impurity in your drinking water. You won’t find this in small under-sink units but a good whole-house filtration system can have it. The system forces water through a membrane, which is a far finer level of filtration than a mesh cartridge. The membrane blocks all sorts of particles and larger molecules, including lead and other heavy metals, leaving you with extremely clean and pure water.

UV Filter

Technically, this is a treatment not a filter since nothing is actually removed from the water with a UV light system. Exposure to ultraviolet light kills any living pathogens, which makes it a good addition to your system if there is a likelihood of organic contamination. Private wells will often have a UV light because there is no chlorine treatment to kill pathogens.


Not as common for home systems, but with the state of our drinking water in question these days, people are looking for better filtering options. Heating water to evaporate, and then letting that vapor re-condense back to liquid results in very pure water because the contaminants don’t evaporate into a gas. They stay behind.

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