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 25 years in industrial coatings filtration and 18 years working with RO, carbon and resin systems, I've seen the water industry change—and watched public trust collapse. Thames Water’s record £122.7 million fine. Brixham’s cryptosporidium outbreak. Financial Times reporting that 16 water monopolies had paid £78 billion in dividends since privatisation. The fine is now only part of the story: by June 2026, BBC reporting described Thames Water as carrying around £20 billion of debt and closer to temporary public ownership through a special-administration regime if a rescue failed. 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. Older property plumbing and ageing infrastructure can affect water quality. The Drinking Water Inspectorate says homes built before 1970 may have lead pipework; risk depends on the individual property’s age and plumbing history. 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 may address: Chlorine taste and odour, some VOCs (volatile organic compounds), some pesticides and some industrial chemicals. For PFAS or any named contaminant, check the exact model’s current certification or performance evidence.
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 may address: Many RO systems are designed for a broad range of dissolved contaminants, such as lead, arsenic, fluoride, nitrates and hardness minerals. However, results vary by system and operating conditions. For lead, PFAS or microplastics, check the exact model’s current certification or performance evidence rather than relying on a category-level percentage.
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 (particularly in 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") | — | Verify model* | — | Verify model* |
| Microplastics | Large only | Large only | — | Verify model* |
| Bacteria/Viruses | Large only | Some | — |
*Note: Filter categories are not performance guarantees. For lead, PFAS or microplastics, verify the exact model’s current certification or performance evidence. For lead reduction specifically, look for a model-specific claim to the relevant standard, such as NSF/ANSI 53 where applicable. Basic carbon filters (like many pitcher filters) should not be assumed to 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, a basic home strip is not a reliable way to establish PFAS or microplastics levels. Meaningful measurement requires appropriate laboratory methods. A filter may be an option, but performance must be checked for the exact system and contaminant.
A July 2025 Guardian investigation found PFAS above proposed safety limits in 110 of 117 English water bodies tested. These are rivers and lakes rather than a measurement of an individual household tap, but the findings show why broad, category-level filter promises are not enough.
Monitoring and reporting arrangements evolve, and they do not provide a routinely published PFAS or microplastics result for every individual tap. If you have a specific concern, ask your water company what it monitors locally and consider an accredited laboratory where appropriate.
What to do next:
Start with your water company’s local water-quality information. If a specific contaminant is your concern, ask what monitoring is undertaken and verify the performance evidence for any filter you are considering.
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.
Do not buy an RO system on a blanket PFAS or microplastics percentage. Compare the exact model’s current performance sheet or independent certification, and make sure it names the contaminant you are concerned about. Our evidence-led PFAS guide explains what to check.
Important: In a hard-water area, check the manufacturer’s pre-treatment advice for the exact RO system. It may recommend a softener or another appropriate pre-treatment step to protect membrane life. See our Water Softeners + RO section for context.
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.
A simple guide to which filter type usually suits which concern.
Best for improving chlorine taste and odour, with no installation needed.
A good middle-ground option for better taste, odour, sediment, and some chemical reduction.
Designed for broader reduction, but performance varies by model and certification.
A broader filtration option; for lead, PFAS, fluoride or microplastics, check the exact model's current performance evidence.
Best for protecting appliances and treating water throughout the home, rather than just at one drinking tap.
Most UK homes do well with a simple under-sink carbon filter or a reverse osmosis system, depending on the concern. If you are worried about lead pipes or broader contaminant reduction, start by comparing certified under-sink and RO options carefully.
Lead is the #1 water quality concern in UK homes built before 1970. These guides will help you understand the risks and solutions.
Homes built before 1970 may have lead pipework; risk depends on age and plumbing history.
NSF 53 certified filters tested. From £35-£400.
4 testing methods compared — including one that's free.
Independent lab data on what Brita actually removes.
Honest comparison with verified certifications and real costs.
Lead protection guide for parents. Budget to best options.
100,000 NI homes affected. Queen's University study.
Lead is not always the only issue people think about. Many UK households are also looking into broader questions around water quality, filtration, and household plumbing.
See our filtration ladder to find the right level of protection for your home—from basic taste improvement to complete contaminant removal.
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.