Water Filters: How Do They Work?
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Water Filters: How Do They Work?

Take a look at the water in your bottle or glass. You'll likely assume that if it's clear, it's probably safe to drink.

Here in America, that, thankfully, is most often the case. However, even the cleanest-looking drinking water contains particles that are too small to be seen with the naked eye. Typically, small amounts of dissolved minerals are present and can alter the taste of the water, but are harmless. However, in developing countries and natural outdoor sources like rivers, these particles can actually be microscopic bacteria, protozoa, and parasites that can make you ill or even kill you. For over 780 million people in the world, these contaminants are a daily struggle.

Thankfully, the water filter was invented to help keep those nasty buggers out of our water and out of our bodies. But how exactly does a filter change a potential poison into something that is necessary to keep us alive?

The concept behind filters is simple: capture all the undesirables and let clean water through. This is accomplished using a material with microscopic pores, or holes. These pores, which can be less than 1/1000th of a millimeter in diameter, let water molecules pass through but are too small for bacteria and viruses to fit.

Municipal Treatment

A variety of materials are used to filter water depending on where it's being filtered. At municipal water treatment plants, water typically first passes through screens made of mesh or other polymers to remove large particles such as sticks, leaves, and other debris. Next, it passes through a series of filters consisting of sand and sometimes even biological filters such as algae to remove smaller contaminants, such as dangerous bacteria and protozoa. Lastly, water is disinfected one of several ways: by adding a small amount of powder or liquid containing chlorine, bubbling in ozone gas, or passing the water through ultraviolet light, which rapidly kills any remaining harmful pathogens that may have passed through the filters. At this point, our water supply is cleaned of large particles and the most dangerous contaminants before they reach our homes.

From Treatment Plant to Home

However, during water's journey from municipal treatment plants to our homes, aging infrastructure can reintroduce contaminants back into our treated water. Aging wastewater systems can leak untreated sewage into our surface waters, and old pipes can leech lead and other heavy metals into the water on the way to our homes. And this is where the residential waters filter plays an important role.

Home Filters

The vast majority of filters used by consumers once the water reaches our homes are made of activated carbon. Activated carbon is popular because just a very small amount has a very large surface area; just a single gram of activated carbon has the surface area of four tennis courts! A large surface area in such a compact volume means there are a greater number of very small pores available to absorb organic compounds and pollutants. PUR water filters use activated carbon made from coconut shells because their pores are even smaller than other types of carbon filters. As a result, a faucet-mounted filter from PUR will remove chlorine; pharmaceuticals and chemicals; heavy metals such as lead and mercury; and other organic compounds that can give water an unwelcome taste and odor. However, it leaves mineral ions such as fluoride, calcium, and magnesium, which are good for the body and even improve the taste of water.

Water filters are the best way to ensure that you're drinking clean, great-tasting water. They're affordable and come in a variety of form factors, such as a pitcher that can sit on your countertop or in the fridge, and a faucet mounts that filters water straight from the tap. They're a must-have for camping or hiking trips so you'll have safe drinking water when you need it.

And water filters are a far better value than bottled water, which costs 14 times as much as filtered tap water and doesn't always taste better than what comes out of the tap. Moreover, bottled water uses lots of environmentally unfriendly plastic; 100,000 cars can run on the amount of oil it takes to produce the plastic for bottled water in a year.

So, filter your water. It's better for your health, for your wallet, and for the environment.

This post was created as part of my collaboration with PUR. As always, all of the opinions, thoughts, and ideas in this post are my own. I am solely responsible for the content.


Scott Jung
Ever since he had atresia surgically repaired at age five, Scott Jung has been fascinated with the field of health and medicine. Combining his love of consumer electronics and technology with medicine, he studied biomedical engineering at the University of Southern California and graduated in 2009. By day, Scott is a Technical Services Engineer at St. Jude Medical, but moonlights as a senior editor at Medgadget, leading health technology and innovation blog.