A complete beginner's guide to understanding water filtration. Learn how different filter types work, what contaminants they remove, and how to choose the right system for your home.
After 20+ years working with reverse osmosis systems, I've seen the water industry change—and watched public trust collapse. Thames Water fined £122.7M. Brixham's cryptosporidium outbreak. £72 billion extracted in dividends while infrastructure crumbles. Your concerns aren't irrational. Let me explain what's actually happening with UK water quality and what you can do about it.
UK tap water is 99.98% compliant with safety standards according to the Drinking Water Inspectorate—when it leaves the treatment works. But what happens between the treatment plant and your tap could be a different story. Victorian-era pipes, lead service lines (1 in 250 UK homes), and aging infrastructure can all affect water quality. Recent incidents like Brixham's cryptosporidium outbreak (May 2024) show the system isn't infallible. I'll explain when you might want a filter—and when you probably don't.
Water filtration isn't magic—it's physics and chemistry. All filters work by passing water through some kind of barrier that traps or removes unwanted substances. But the type of barrier determines what gets removed and what doesn't.
Think of it like a series of sieves with different-sized holes. A colander catches pasta but lets water through. A coffee filter catches grounds but lets coffee through. Water filters work the same way—just at a microscopic level.
How it works: Water passes through a physical barrier (like a screen or membrane) that traps particles larger than the pore size. Think of it as a very fine sieve.
What it removes: Sediment, rust, sand, silt, dirt, and visible particles. The finer the filter, the smaller the particles it catches.
Examples: Sediment filters (5-50 micron), ceramic filters (0.5-0.9 micron absolute), some membrane filters.
Ceramic Filters (Doulton, British Berkefeld): A special type of physical filtration using microporous ceramic (diatomaceous earth). The 0.5-0.9 micron pores trap bacteria (>99.99%), cysts (Giardia, Cryptosporidium), and sediment. Many include an activated carbon core for chlorine and taste removal.
Best for: Off-grid living, well water, emergency preparedness (no electricity needed). Popular in the UK for gravity-fed countertop systems. See our ceramic filters guide for details.
What's a micron? Most people have no idea. Here's the scale:
So a 5-micron filter catches particles smaller than a red blood cell. A 50-micron filter catches anything larger than half the width of a human hair.
Real talk: These are great for protecting other filters and removing visible gunk, but they won't remove dissolved contaminants like lead, chlorine, or chemicals. If your water looks clear, a sediment filter alone won't do much.
How it works: Water passes through a porous material (usually activated carbon) with a massive surface area. Contaminants chemically bond to the surface and get stuck there.
What it removes: Chlorine (95%+), taste, odor, some VOCs (volatile organic compounds), some pesticides, and some industrial chemicals. Specialized carbon can remove some PFAS.
Examples: Activated carbon filters (granular or block), carbon block filters.
Real talk: This is the most common and cost-effective filter type. Perfect for improving taste and removing chlorine smell. But it won't remove minerals (hardness), lead, arsenic, fluoride, or nitrates. Be skeptical of claims that a basic carbon filter removes "99% of contaminants"—most don't.
How it works: Water passes through resin beads that swap "bad" ions (like calcium, magnesium, lead) for "good" ions (like sodium or hydrogen). It's a chemical trade.
What it removes: Hardness minerals (calcium, magnesium), some heavy metals (lead, copper), nitrates (with specialized resin).
Examples: Water softeners (most common), some lead removal filters, nitrate removal systems.
Real talk: Water softeners are great for protecting appliances from limescale in hard water areas (like London and South East England). But Thames Water advises against drinking softened water because it adds sodium. If you have a softener, install a separate tap for drinking water or use an RO filter.
How it works: Water is forced through a semi-permeable membrane with pores so tiny (0.0001 micron) that only water molecules can pass through. Everything else gets flushed away or trapped within the filter.
What it removes: Lead (99%+), arsenic, fluoride, nitrates, PFAS (90%+), microplastics (99%+), bacteria, viruses, hardness minerals, chlorine, and 95-99% of all dissolved solids. It's the most comprehensive filtration method available.
Examples: Under-counter RO systems, countertop RO units, whole-house RO (rare/expensive).
Real talk: RO is the gold standard for comprehensive protection, especially if you're concerned about lead (pre-1970 homes), PFAS, or microplastics. Downsides: wastes 3-4 gallons per gallon produced, removes beneficial minerals (not a health concern—you get minerals from food), and costs £200-£500. Worth it if you have specific contamination concerns or want the most thorough protection.
| Contaminant | Sediment | Carbon | Softener | RO |
|---|---|---|---|---|
| Sediment/Rust/Sand | — | |||
| Chlorine (taste/odor) | — | — | ||
| Lead | — | Partial* | Partial | |
| Hardness (Ca/Mg) | — | — | ||
| Fluoride | — | — | — | |
| Nitrates | — | — | Special resin | |
| PFAS ("forever chemicals") | — | Special carbon | — | |
| Microplastics | Large only | Large only | — | |
| Bacteria/Viruses | Large only | Some | — |
*Note: Only NSF-certified carbon block filters remove lead effectively. Basic carbon filters (like pitcher filters) don't remove lead reliably.
Remember: UK water is 99.98% compliant with safety standards when it leaves the treatment works. You don't need a filter just because someone's trying to sell you one. But there are legitimate reasons to filter your water:
Bottom line: Don't buy a filter because of fear or marketing hype. Buy one to solve a specific problem you've identified: lead pipes in your home, chlorine taste/odor, hard water limescale, PFAS 'forever chemicals', microplastics found in human organs, or other documented contaminants. Compare filter types to find the right solution for your specific issue.
At the time of writing, you cannot test for PFAS or microplastics at home. The technology requires specialized laboratory equipment costing thousands of pounds. But you CAN remove them.
A 2024 Guardian investigation found PFAS above proposed safety limits in 110 of 117 English water bodies tested. These are the rivers and lakes where families swim, boat, and fish—yet many residents were unaware of the contamination levels until the investigation was published.
While water companies are required to monitor PFAS and microplastics in tap water, no home testing kits exist for these contaminants. In other words, you're relying entirely on your water company's voluntary testing—with no way to verify their results yourself.
Scotland vs England:
Why the difference? That's a question worth asking your local water company. You can contact them directly to ask:
Find your water company contact details on their website or via Ofwat's directory.
Reverse osmosis systems filter out 95-99% of both PFAS and microplastics—giving you control over what your family drinks, regardless of what's in the mains supply.
Important: If you live in a hard water area (London, South East, East Anglia), you'll also need a water softener installed BEFORE your RO system. Hard water reduces RO membrane lifespan by up to 30%. See our Water Softeners + RO section for full details.
Reverse osmosis removes minerals (calcium, magnesium), but water softeners and carbon filters don't. Here's the truth: you get 99% of your minerals from food, not water. The amount of calcium in a glass of milk equals 30 glasses of hard water. If you eat a balanced diet, removing minerals from water is not a health concern. Some people prefer to add minerals back for taste—that's fine, but it's not necessary for health if you maintain a balanced diet. If you have dietary restrictions, consult your doctor or health advisor. Learn more about RO systems.
It depends on the filter type and your water usage. Sediment filters: 3-6 months.Carbon filters: 6-12 months. RO membranes: 2-3 years.Softener resin: 10-15 years (just refill salt). Don't skip filter changes—a saturated filter can't remove contaminants and may release trapped contaminants back into your water.
Pitcher filters use basic granular activated carbon. They're good for: improving taste and removing chlorine. They're NOT effective for: lead removal (unless NSF-certified for lead), hardness, fluoride, nitrates, PFAS, or microplastics. They're a budget option for taste improvement, but don't expect comprehensive protection. If you have lead pipes or specific contamination concerns, invest in a proper under-counter system.
In the UK, these terms are used interchangeably. Technically, "purifiers" remove microbiological contaminants (bacteria, viruses) while "filters" remove physical and chemical contaminants. Reverse osmosis systems are both filters and purifiers. UV sterilizers are purifiers but not filters (they kill microbes but don't remove chemicals). For UK tap water, which is already microbiologically safe (99.999% E. coli compliance), you typically need a filter, not a purifier.
Countertop and pitcher filters: Yes, anyone can do this. Faucet-mount filters: Yes, simple DIY.Under-counter filters: Possible for DIY if you're handy (requires drilling, connecting to cold water line).Whole-house systems and softeners: Hire a plumber—these require professional installation and may affect your home insurance if installed incorrectly. Always follow manufacturer instructions and local plumbing codes.
Now that you understand how filters work, let's figure out which one you actually need.
From basic taste improvement to complete home protection — see what each level removes
Basic chlorine & taste improvement
Chlorine, taste & basic contaminants
Lead, PFAS, microplastics & more
Near-complete contaminant removal
Every tap protected + appliance life
💡 Most UK homes benefit from Level 2-3. Lead pipes or health concerns? Consider Level 3-4.
Lead is the #1 water quality concern in UK homes built before 1970. These guides will help you understand the risks and solutions.
Lead often isn't the only concern. Many UK homes face multiple water quality issues.
Compare carbon, RO, UV, and softeners to find the right system for your needs.
Find out what's in your tap water and which contaminants to filter for.
Learn what NSF, WQA, and WRAS certifications actually mean.
Do you really need a £500 whole-house system? Probably not.