Water filter type
Under-sink carbon filters
A carbon block cartridge on the cold line under the sink. The simplest way to improve drinking water taste, and with the right certification it also covers lead.
The cheapest thing that usually works
For most households on municipal water whose complaint is taste, a carbon block under the sink solves the problem for a fraction of what a larger system costs. It is the option we recommend most often, and it is the one with the smallest margin in it.
Carbon works by adsorption. The block has an enormous internal surface area, and organic molecules including chlorine by-products stick to it as water passes. Contact time matters, which is why a dense block outperforms a loose granular cartridge at the same size.
It connects to the cold line under the sink and feeds either the existing mixer or a small dedicated tap, depending on the model and how much space the cabinet has.
Certification is the whole decision
Two filters that look identical can do very different jobs. A cartridge certified only under NSF/ANSI 42 has been tested for aesthetic effects, mainly chlorine, taste, and odour. It has not been tested for lead.
Lead reduction is NSF/ANSI 53. Cyst reduction is also 53. Pharmaceuticals and incidental compounds fall under NSF/ANSI 401. A product that claims to reduce contaminants without naming a standard has told you nothing you can check.
When someone asks us to fit a filter they already bought, this is the first thing we look up. It is also where most online purchases go wrong, because the listing language is designed to imply coverage the certification does not support.
Replacement is not optional
A saturated carbon block stops working, and in some conditions can release captured compounds back into the water. That is genuinely worse than having no filter, because you are drinking with a false sense of protection.
The rated capacity is in gallons, not months. A household of five hits it far sooner than a household of one. When we hand over, we put the date on the housing and tell you which cartridge to buy, including part numbers you can source yourself.
You do not need a service contract with us to keep it working. Most people change these themselves in about ten minutes.
What it reduces, and under which standard
Each row names the NSF/ANSI standard the category is tested under. A standard describes what the test covers. It does not mean every unit on the market carries that certification, so check the specific model against its listing before you buy.
| Contaminant | Standard | Note |
|---|---|---|
| Chlorine taste and odour | NSF/ANSI 42 | |
| Lead | NSF/ANSI 53 | Only on models certified to 53 for lead. A 42-only filter does not reduce lead. |
| Cysts | NSF/ANSI 53 | |
| Volatile organic compounds | NSF/ANSI 53 | |
| Pharmaceuticals and incidental compounds | NSF/ANSI 401 |
What it does not do
Every filter has a boundary. These are the things this one will not fix, listed so you can rule it out quickly if your problem is on the list.
- Hardness and scale.
- Nitrates, fluoride, and most dissolved salts.
- Bacteria and viruses.
- Anything at all once the cartridge is saturated, which is why the replacement date matters more than the brand.
When it fits
- Chlorine taste is the main complaint
- You need lead reduction at one tap in an older building and want the least invasive option
- You want low running costs and no drain connection
When it does not fit
- The problem is nitrates, arsenic, or high dissolved solids
- You need treated water at every tap
- The water is not microbiologically safe
Space, services, and upkeep
A single housing, roughly 4 by 14 inches, mounted inside the cabinet.
No drain connection is required. It needs no power. In the right configuration this can work in a rental, because it does not have to permanently alter the property.
Replacement interval. Every 6 to 12 months, or sooner if flow drops noticeably.
Problems this is used for
We recommend this equipment against these confirmed problems. Each page explains how to confirm the problem before spending anything, and when treatment is not warranted.
- Chlorine and chloramine taste. Utilities add a disinfectant residual and are required to maintain it through the distribution network.
- Lead in drinking water. Lead does not normally come from the source water.
- PFAS. A large family of manufactured fluorinated compounds used in firefighting foam, non-stick coatings, and industrial processes.
Property types where this comes up
- Brownstones and pre-war buildings
- Co-ops and condos
- Rentals
- Single-family homes on city water
- Offices
- Medical and dental practices
Common questions
What is the difference between NSF/ANSI 42 and 53?
Standard 42 covers aesthetic effects, which in practice means chlorine, taste, odour, and particulates. Standard 53 covers health effects, including lead, cysts, and volatile organic compounds. A filter certified only to 42 has not been tested for lead. The two products can look identical and sit next to each other on a shelf, so the certification is the only way to tell them apart.
Do I need a separate tap?
It depends on the model. Some inline cartridges feed the existing mixer so all your cold water is filtered, which uses cartridges faster. Others feed a small dedicated tap, which concentrates the filter's capacity on drinking and cooking water. If your worktop has no spare hole and you cannot drill one, the inline option is the one that works.
Can I change the cartridge myself?
Almost always, and most people do it in about ten minutes. You close the inlet valve, relieve the pressure, swap the cartridge, then run the tap for a few minutes to flush carbon fines before drinking. We leave the part numbers with you so you can buy cartridges from whoever you like. You do not need a service contract to keep the filter working.
Other filter types to compare
If the notes above rule this out, these are the neighbouring options worth reading before you decide.
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