How Do Water Filters Work?

Water filters work by passing tap water through one or more materials that physically catch particles, chemically bind contaminants, or neutralise microbes. 

There isn’t one single method that does everything – what gets removed depends on the type of filter you’re using. 

If your tap water smells a bit like chlorine or just tastes off, that’s usually the kind of issue a water filter is there to improve.

Let’s explore how they work in more detail. Read on for more information on what water filters do, the different types, and how they work. 

What Does a Water Filter Do?

A water filter separates unwanted substances from your drinking water – which could include visible debris, dissolved chemicals, microscopic organisms, or heavy metals. 

In 2022, 77% of Americans said they filter their drinking water at home, up from 73% in 2020 – and by 2023, that figure had risen to 91%. It's a mainstream habit, and for good reason.

Water filters usually have several processes. Even a simple jug filter usually combines a couple of stages – for example, one to catch larger particles, and another to deal with taste and chemicals.

As water flows through the filter, different layers do different jobs:

• A mesh or sediment layer traps bits you can often see (e.g. sand, rust, scale, etc)
• Carbon media improves taste and removes things like chlorine
• Finer membranes or specialised stages handle smaller or dissolved contaminants

If you want a deeper look at how different systems compare, it’s worth reading more about the different types of water filters.

Types Of Water Filters (And How They Compare)

Here’s a quick and easy way to see how the main types of water filter differ in practice:

Sediment Filtration

This is the simplest kind of filtration. Water passes through a physical barrier (usually a fine mesh or fibre layer) which catches solid particles. Sediment filtration is usually the first stage in many systems. It stops grit or rust from clogging more delicate filters further down the line.

Although this method is useful, it’s also limited – it won’t touch chlorine, metals, or anything dissolved.

Carbon Filtration

Carbon filters are the reason filtered water often tastes noticeably better. They use activated carbon, which has a huge surface area full of tiny pores. Contaminants stick to that surface as water passes through – which is a process called adsorption.

This is especially effective for:

• Chlorine (the “swimming pool” taste)
• Volatile organic compounds (VOCs)
• Some pesticides and chemicals
  

 

Carbon filtration alone does not remove everything – so if you’re expecting a carbon filter to deal with heavy metals or bacteria on its own, you’ll likely be disappointed.

If you want to know more about carbon filtration and how it works, we have a helpful guide on what carbon filters remove from water. 

Reverse Osmosis (RO)

Reverse osmosis systems push water through an extremely fine membrane – only water molecules can pass through easily, and most dissolved solids get left behind. This makes RO one of the most thorough filtration methods available for home use.

RO is ideal if you want to reduce:

• Heavy metals like lead
• High levels of dissolved salts
• Nitrates and similar contaminants

However, reverse osmosis is slower, produces some wastewater, and removes beneficial minerals along with the unwanted ones.

UV Filtration

UV systems don’t remove particles or chemicals – instead, they use ultraviolet light to disrupt the DNA of bacteria and viruses, stopping them from reproducing. UV filtration is usually added as a final stage of filtration, after other filters have already cleaned up the water physically.

On their own, they’re not enough – but paired with other filtration, they can add an extra layer of protection.

Ion Exchange

Ion exchange is mostly used in water softeners. It works by swapping calcium and magnesium ions (which cause limescale) with sodium or hydrogen ions – which is why softened water helps prevent scale build-up in kettles and pipes.

Note – this method doesn’t really deal with taste, chlorine, or contaminants — it solves a different problem.

 

Chemical vs Physical Filtration

Physical filtration is straightforward; it blocks or traps particles. Sediment filters and membranes fall into this category.

Chemical filtration changes or captures contaminants at a molecular level. Carbon filters are the main example here.

Here are the key differences between chemical and physical filtration: 

Most effective systems combine both – a purely physical filter won’t fix taste or dissolved chemicals, and a purely chemical approach will struggle to filter larger debris.

What Do Water Filters Remove?

What water filters remove depends entirely on the setup you’re using. In everyday terms, water filters usually target a mix of:

• Chlorine and compounds that affect taste and smell

• Sediment like rust or sand

• Heavy metals such as lead (in some systems)

• Organic chemicals

• Microorganisms (with UV or specialist filters)

What often surprises people is what filters don’t remove unless specifically designed to. For example, not every filter handles bacteria, and not every filter removes microplastics.

Whole-House vs Point-of-Use Filters

Whole-house systems treat water as it enters your home – so every tap, shower, and appliance uses filtered water. This type of system tends to include sediment filters and sometimes carbon or softening systems.

Point-of-use filters sit where you actually drink the water – for example, kitchen taps, under-sink systems, or filter jugs.

For most people, a point-of-use filter is enough. This type of filter targets your drinking water directly, which keeps things simpler and more affordable. 

Which is best for you? Whole-house systems make more sense if you’re dealing with broader issues like heavy sediment, strong chlorine throughout the home, or hard water affecting plumbing. Point-of-use filters are ideal for everyday use to target your drinking water directly. 

Improve Your Drinking Water with PIURIFY

If your main concern is taste and everyday contaminants, you don’t need a complicated whole-house system. A water filter pitcher should do just the trick. 

The Alchemy Automatic Water Filter Pitcher filters as you use it, doesn’t require installation, and focuses on the things you will actually notice – cleaner taste, reduced chlorine, and better overall drinking water. 

With our filter pitcher, you can save $1,000 USD per year, and avoid using around 2,000 plastic bottles. 

If you’re still weighing things up, check out our guide on whether filtered water is good for you!