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How Do Home Water Filters Work?

Published by: Chef Amy Hand • Updated: January 24, 2024 • Checked By: Chef Matty Riedel

Some see the need for home water filters as a waste of time because their local authority has deemed tap water safe to drink. Those aware that unseen water elements may harm their health are on the other side of the debate. If you’ve ever experienced bad-tasting water that smells (chlorine) or is cloudy and has other visible matter present, you probably now own a water filter. If you don’t own a water filter and have ever wondered “how water filters work”, read on.

How Do Water Filters Work?

Most water filter systems work in essentially the same way. Water passes through a removable cartridge filled with a filtering medium such as activated charcoal.

Water treatment plants use two types of filtration: physical and chemical. Physical filtration involves pushing the water through a fine mesh to catch larger particles, while chemical filtration uses activated carbon to absorb contaminants like chemicals and organic matter.

These techniques are also present in our home water filters, just on a smaller scale, to catch anything the treatments may have missed and to filter out any harmful additives added to the water during this process.

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Types of Home Water Filters Available:

If you want a filter at home, you have two several options:

  • Water pitcher filter
  • On-tap filter
  • Countertop filter
  • Undersink water filter
  • Reverse Osmosis
Doulton Undersink Water Filter with Sediment Filter
Doulton Undersink Water Filter with Sediment Filter

Undersink and Countertop Water Filters

We looked at Brita vs Berkey water filters in an earlier post. Berkey is a great example of a countertop water filter. These and under-sink filters do a much better job of removing impurities from your town water than a water jug or on-tap filter will ever do.

If you are serious about drinking clean water (and why wouldn’t you be?), a countertop or under-sink water filter is the way to go. The contaminants these filters can remove are far superior to those of a water filter or on-tap unit. Many of these filters struggle to remove chlorine, which is probably the easiest chemical to remove! Fill your kettle with filtered water and enjoy a seriously good cup of tea (or coffee)

Water Jugs & On-Tap Filters

All you do for the pitcher is fill it with water and place it in your fridge, and the spout, fitted with the filter, will treat your water as you pour each glass. An on-tap filter is fitted to your existing tap, and the water is filtered right as it comes out; some even come with a special shower filter to wash vegetables with clean water. The water pitcher options are the most commonly used because they are more affordable and can be popped into the fridge without installation. 

These filters may appear very different, but they are, in fact, the same when it comes to how the water is filtered. The key to both of these designs is activated carbon. The carbon is cylindrical, giving it a sizeable exterior surface area, so the water is passed through the outer layer and pours out through the centre, leaving all the unwanted stuff behind. But why activated carbon, you might ask? When activated, this particular substance becomes very porous and can absorb contaminants like chlorine, pesticides, and other organic matter. So the filter is essentially a collection of spherical particles that act like a magnet that attracts all these different substances, including metals like lead, mercury or copper and traps them within it.

Some Of The Contaminants Removed By A Good Water Filter

  • Chlorine
  • Heavy Metals
  • Bacteria
  • Volatile Organic Compounds such as pesticides and herbicides
  • Rust particles (from ageing pipe infrastructure)
  • Microplastics
One Of The Biggest Nasties You’ll Come Across: Cryptosporidium Parvam

Activated Carbon, Ion Exchange & Reverse Osmosis

The only things carbon doesn’t attract and eliminate are nitrates and bacteria, as they don’t bind with it, but treatment at the water plant should handle these issues. The most common material these carbon filters are made from is coconut shells because they are the most efficient and eco-friendly, but they can also be made from coal, wood or other high-carbon nut shells. They can catch any 2 microns in size or larger substances to catch microplastics and even some bacteria.  

Some filters also use an ion exchange system, which uses resin to reduce the water’s hardness and filter out calcium and magnesium, but they are not as common. Another less common method is reverse osmosis, which pushes the water through a semipermeable membrane that can prevent dissolved solids from passing through. This is very effective and removes most contaminants. Still, it also removes the healthy minerals naturally present in water, which is a significant downside as water is an easy way to get some iron, potassium, sodium and zinc into your diet, among others. A decent reverse osmosis system can add a mineral filter to return small amounts of healthy minerals to your water.

Why Use A Water Filter? 

Your tap water may look pure but contain invisible contaminants that may not be doing you any health favours. These particles could be anything from microplastics in 90% of our tap water. Metals are present due to old or corroded pipes, organic matter, and harmful chemical additives from the town water treatment process.  

In most cases, a filter will also help improve the flavour in areas with higher levels of chlorine or minerals, affecting what the water tastes like and sometimes making it cloudy. In addition, filtering your tap water means that you can drink the water supplied to your home instead of buying bottled water, which will save you money and be more environmentally friendly as it will help you reduce your plastic waste. 

How Do Water Filters Work: Summing Up

A water filter is the last line of defence for those concerned about water quality to give them peace of mind. If you think about it, there’s no way of us knowing 100% what’s in our water and using a filter can combat all these unknowns.

Chef Amy Hand