Stop thinking water purifiers are ‘mysterious’! Understand in 3 steps how they turn dirty water clean

When your home water purifier hums away, have you ever wondered: how does a cup of dirty water become pure, drinkable water? This little machine isn't performing magic—it's a clear ‘water purification assembly line’.

Today we break down its working principles in 3 steps, banishing the frustration of ‘not understanding how it works or how to choose one’.

01 Step One: Understand the Core ‘Filtration Team’ – Each Component Has a Dedicated Task

The purification capability of a water purifier relies entirely on the collaborative efforts of its multi-layered filter cartridges, forming a ‘filtration team’. Much like an assembly line in a factory, each stage tackles a specific issue, progressively ensuring water quality.

Pre-filter: The coarse-filtering ‘gatekeeper’ The outermost PP cotton filter acts as the first line of defence. Resembling a white cotton swab, it primarily intercepts visible large particles like silt, rust, and insect eggs. Functioning like a household window screen, it blocks ‘bulky’ contaminants upfront, preventing clogging of subsequent fine filters. Typically requiring replacement every 3-6 months, it is the most frequently replaced consumable.

Core Filter: The Precision ‘Main Filter’ This is the heart of the water purifier, with mainstream technologies divided into two types:

RO Reverse Osmosis Membrane Filter: Dubbed the ‘microscope of filtration,’ with pore sizes of just 0.0001 micrometres (one millionth the width of a human hair). It removes nearly all microscopic contaminants like heavy metals, bacteria, and viruses, producing water safe for direct consumption. Households with elderly members or children predominantly opt for this technology.

Ultrafiltration Membrane Cartridge: With a pore size of approximately 0.01 micrometres, it filters out bacteria, colloidal impurities, and other contaminants while retaining essential minerals in the water. Suitable for households with relatively good water quality who prioritise ‘mineral retention’.

Core filter cartridges have a relatively long lifespan. RO membranes typically last 2-3 years, while ultrafiltration membranes last 1-2 years, depending on water quality and usage volume.

Post-filter: The taste ‘optimiser’ The final layer of activated carbon filter handles the ‘finishing touches’, primarily adsorbing residual chlorine odours and improving taste to make purified water sweeter. This difference in taste is more noticeable when brewing tea or coffee. Its replacement cycle is generally 6-12 months.

02 Step Two: Understanding the Water Purification Process – Witnessing Water Quality Transformation in Three Stages

With an understanding of the filter stages' roles, the water purification process becomes much clearer. Taking the most common RO reverse osmosis water purifier as an example, a glass of water undergoes three key stages:

1. Coarse Filtration: First ‘sifting out’ large impurities. Tap water first enters the PP cotton filter cartridge, where large particles like silt and rust are rapidly intercepted. This step is akin to ‘rinsing off surface dust’ from fruit, making subsequent filtration more efficient. After coarse filtration, the water transforms from “cloudy” to ‘clear,’ though it remains undrinkable.

2. Fine filtration: Precisely ‘removing’ micro-contaminants. The clarified water then enters the RO reverse osmosis membrane (or ultrafiltration membrane), the most critical stage. The RO membrane acts like a ‘super filter’, blocking invisible contaminants like heavy metals (e.g., lead, mercury), bacteria, and viruses while allowing only water molecules and trace beneficial minerals to pass through. This step effectively performs ‘deep disinfection and purification,’ elevating the water to direct-drinking standards.

3. Enhanced Taste: Final ‘Flavour Refinement’

The refined water then passes through an activated carbon filter, where residual chlorine odours and other unpleasant tastes are thoroughly adsorbed. The resulting water is not only pure but also boasts a sweeter, crisper taste, making it more reassuring for both direct consumption and cooking.

The entire process relies on the water purifier's pump to drive water sequentially through each filter layer. The fully enclosed, contact-free system prevents secondary contamination. Now, when you look at the water purifier under your sink, doesn't it seem more like a miniature water quality optimisation plant?

Step 3: Avoid common pitfalls in selecting models and choose the right water purification solution based on your needs

Once you understand the principles, selecting a water purifier won't involve blindly following trends. Remember these three core principles to easily choose the right model for your home:

✅ Assess household needs: Select technology based on usage scenarios

Households with infants, pregnant women, or the elderly: Prioritise RO reverse osmosis systems for thorough purification, ensuring peace of mind when preparing infant formula or drinking directly.

Areas with good water quality (e.g., some southern cities) or those wishing to retain minerals: Consider ultrafiltration systems for better value for money.

Renters or small-space dwellings: Opt for countertop, no-installation water purifiers. No drilling or wiring required—simply plug in and use, making relocation hassle-free.

✅ Filter cartridge costs: Calculate the long-term value

Beyond the initial purchase price, consider replacement cartridge expenses. Reputable brands offer transparent pricing—for instance, a mainstream RO system's annual cartridge replacement costs around £20-£30, averaging less than £1 daily, making it more economical than bottled water. Avoid niche brands with scarce, overpriced cartridges.

✅ Consider practical features: prioritise ‘low-maintenance models’

With ‘filter life alerts’: no need to track replacement schedules – the machine automatically notifies you, ideal for beginners;

With ‘wastewater ratio adjustment’: premium models achieve a 2:1 ratio (producing 2 cups of purified water for every 1 cup of wastewater), saving water;

Features ‘UV sterilisation’: Ideal for humid regions, preventing bacterial growth in filters for enhanced water quality.

The principle behind water purifiers is actually quite straightforward. Essentially, they employ a ‘layered filtration’ approach to make water purer and more palatable. Much like how we layer clothing with ‘base layers + outerwear’ for protection, water purifiers combine ‘coarse filtration + fine filtration + taste optimisation’ to safeguard your household's drinking water quality.