Find the filter that fits your water.

Two questions decide almost everything

The first is what you are trying to remove. The second is where you want the water treated. Answer those two and the list of sensible options usually drops from seventeen to two or three.

Point-of-entry equipment sits on the main line and treats everything in the building. Point-of-use equipment treats one tap. People often assume point-of-entry is simply the better version because it covers more outlets, and for chlorine or sediment that is broadly right. For lead it is close to backwards, because lead enters the water from the pipework between the main line and the tap, which means a filter at the point of entry sits upstream of the problem.

The same logic applies to cost. Treating one tap is cheaper to install and cheaper to maintain, and for drinking water it usually covers more contaminants than a whole-building carbon filter does.

Start from a confirmed problem

Choosing equipment before testing is the most expensive mistake in this field. A softener fitted against a lead worry does nothing about lead. A carbon filter fitted against nitrates does nothing about nitrates. Both keep costing money every time a cartridge is replaced.

• Hard water. Confirm with hardness test strip or titration kit, in grains per gallon.
• Chlorine and chloramine taste. Confirm with free and total chlorine test strip, plus the utility report for the disinfectant type.
• Lead in drinking water. Confirm with certified laboratory analysis of a first-draw tap sample.
• PFAS. Confirm with certified laboratory analysis using an epa-approved pfas method.
• Iron and rust staining. Confirm with laboratory iron panel, distinguishing dissolved from oxidised iron.
• Sulfur smell. Confirm with laboratory hydrogen sulfide test, after isolating hot from cold.
• Sediment and cloudy water. Confirm with glass settling test, then a turbidity reading if it persists.
• Bacteria in well water. Confirm with laboratory total coliform and e. coli test, annually at minimum.

Each of those pages includes a section on when not to treat, because for several of these problems the correct answer is a habit change, a call to your utility, or a repair to something other than the water supply.

Treatment at the point of entry

These systems sit where water enters the building. They suit whole-building problems: scale, sediment, iron staining, corrosive water, and disinfection on a private well.

• Whole-house filtration. A filter plumbed into the main line where water enters the building, so every tap, shower, and appliance downstream is fed treated water.
• Water softeners. An ion exchange system that swaps calcium and magnesium for sodium or potassium, which is the only method that actually removes hardness minerals from the water.
• Salt-free conditioners. Template assisted crystallisation changes how hardness minerals behave so they are less likely to stick as scale.
• Ultraviolet disinfection. A lamp that inactivates bacteria, viruses, and protozoa as water passes through.
• Iron and manganese removal. Oxidation followed by filtration, sized to the form and concentration of iron present.
• Sulfur and hydrogen sulfide treatment. Oxidation and filtration aimed at the rotten egg smell.
• Acid neutralisers. A calcite or magnesia bed that raises the pH of acidic water, which stops it dissolving copper out of the pipes it runs through.
• Sediment filters. A mechanical filter that captures sand, silt, rust flakes, and other particles.
• Well water systems. A treatment train assembled around a current laboratory test, in stages.

Treatment at the tap

These treat drinking and cooking water at a single point. For health contaminants this is usually both the more effective and the cheaper choice.

• Reverse osmosis, tank. A membrane system under the sink that produces treated water to a dedicated tap and stores it in a small pressure tank.
• Reverse osmosis, tankless. A pumped membrane system that produces water on demand rather than storing it, so it takes far less cabinet space and can sit on a counter.
• Under-sink carbon filters. A carbon block cartridge on the cold line under the sink.
• PFAS reduction systems. Reverse osmosis or a certified activated carbon system aimed at per- and polyfluoroalkyl substances.
• Lead reduction filters. Point-of-use filters certified for lead under NSF/ANSI 53.

Commercial equipment

In commercial settings the specification is usually driven by equipment protection, throughput, and documentation requirements rather than by taste.

• Bottleless water coolers. A cooler plumbed into the building supply with filtration built in, replacing delivered bottles.
• Commercial ice machine and beverage filters. Scale and chlorine control sized to the throughput of ice machines, coffee brewers, and beverage dispensers.
• Drinking fountain and bottle filler filters. Filters fitted to fountains and bottle fillers in schools, offices, and public buildings.

If you rent

Anything that permanently alters the property needs your landlord's written agreement. These are the options that generally do not, or that can be configured so they do not.

• Reverse osmosis, tankless
• Under-sink carbon filters
• PFAS reduction systems
• Lead reduction filters

More on this in filters for rentals, including what tends to be acceptable to a landlord and what is not worth asking for.

How to read a certification claim

NSF/ANSI standards are the only reliable way to compare products, and each number covers a different job. Standard 42 covers aesthetic effects, mainly chlorine, taste, and odour. Standard 53 covers health effects including lead, cysts, and volatile organic compounds. Standard 44 covers ion exchange softeners. Standard 55 covers ultraviolet systems. Standard 58 covers reverse osmosis. Standard 401 covers incidental compounds such as pharmaceutical residues, and protocol P473 was written specifically for PFOA and PFOS.

A product certified under 42 alone has not been tested for lead. This matters because the two filters can look identical and sit next to each other on a shelf. When a listing says a filter reduces contaminants without naming the standard and the specific contaminant, it has given you nothing you can verify.

Certification is also per model rather than per brand. A manufacturer with certified products in its range may also sell uncertified ones. If you have already bought something and want to know what it actually covers, send us the model number and we will look up its listing before we quote for fitting it.