In short
- The four types differ mainly in where they sit: on the counter, on the tap, under the sink or on the pipe where water enters the house.
- Renters and small kitchens usually start with the options that need no plumbing; owners with space can consider fixed systems.
- Reverse osmosis is a separate kind of system, usually installed under the sink, and it usually needs a storage tank or a pump.
- No type is free of upkeep, so think about who will change the cartridges before you think about installation.
- A filter page cannot answer a question about your own water; your local water utility or a certified laboratory can.
Home water filters come in four common forms, and the main difference between them is where they sit: on the counter, on the tap, under the sink, or on the pipe where water enters the house. That one fact decides how you install them, who can use them, how much space they need and how much upkeep they ask for. This guide compares them in plain words. It does not rank them, because the right one depends on your home, your plumbing and what you want from your water.
The four types in plain words
Pitchers and countertop dispensers. A filter pitcher has a replaceable cartridge in its lid or upper section. You pour tap water into the top, it passes through the cartridge, and it collects in the lower section, ready to pour. A countertop dispenser works in a similar way, with a larger container and a small tap. There is no plumbing. You do the work by hand: refilling, changing the cartridge on schedule and washing the container as the maker describes. See Pitchers & Countertop for the range.
Faucet filters. A faucet filter is a small unit that attaches to the end of the kitchen tap. Many have a switch that lets you choose between filtered and unfiltered water, which is handy if you only want filtered water for drinking and cooking. Whether one fits depends on the shape and thread of your faucet, and pull-out or spray faucets are not always compatible, so read the fitting information on the product page. Many can be fitted by hand, but follow the instructions. You will find them under Faucet Filters.
Under-sink filters. These sit in the cabinet below the sink and connect to the cold water line. The water is filtered before it comes out, either through your existing tap or, in many setups, through a separate small faucet fitted to the sink or counter. Installation involves plumbing connections and sometimes a hole for that extra faucet, so renters should check their lease first. Upkeep means opening the housings and changing the cartridges inside. See Under-Sink Filters.
Reverse osmosis (RO). Reverse osmosis is a different kind of system rather than a fifth location. It works by pushing water through a very fine membrane, a thin sheet with extremely small openings. The process is slow, so most home systems include a storage tank that fills between uses, or a pump. RO systems are usually installed under the sink, with a small faucet of their own, and many also connect to a drain line. Many have several stages, each with its own cartridge or membrane, so expect more parts to look after than with a basic filter. If you are unsure about the installation, ask a licensed plumber. See Reverse Osmosis Systems.
Whole-house filters. A whole-house system is fitted to the main water line where water enters the building, so the filtered water reaches every tap, shower and appliance on that line. It uses large housings and cartridges, needs an accessible length of pipe plus wall or floor space, and is normally installed by a licensed plumber. Because it changes the plumbing of the building, it generally suits owners, and renters would need the landlord's permission. See Whole-House Filters, including Sediment & Carbon Systems and Well Water Systems.
Side by side
| Type | Where it goes | Installation | Upkeep | Space |
|---|---|---|---|---|
| Pitcher or countertop dispenser | Refrigerator shelf or counter | None; prepare the cartridge as instructed | Refill by hand, change the cartridge on schedule, clean the container | Shelf or counter space |
| Faucet filter | On the end of the kitchen tap | Attaches to the faucet; fit depends on the faucet | Change the cartridge or unit on schedule | Very little |
| Under-sink filter | Sink cabinet, on the cold water line | Plumbing connections, sometimes an extra faucet | Change cartridges in their housings on schedule | Cabinet space |
| Reverse osmosis system | Usually under the sink | Plumbing connections, usually a drain line and a tank or pump | Several cartridges and a membrane, each on its own schedule | Cabinet space plus room for a tank |
| Whole-house system | Main water line, where it enters the house | Plumbing work, often by a licensed plumber | Larger cartridges, changed on schedule | Wall or floor space near the main line |
Who each type tends to suit
- Renters: pitchers, countertop dispensers and faucet filters, because they need no changes to the plumbing. An under-sink system may be possible with your landlord's permission.
- Small kitchens: a faucet filter takes almost no room, and a pitcher needs a refrigerator shelf or a corner of the counter. An under-sink system needs a cabinet that is not already full.
- Families: a household that drinks and cooks with a lot of water may find refilling a pitcher a chore, so a tap-based or under-sink system can be easier to live with. A whole-house system also covers showers and appliances, not just the kitchen.
- Houses on well water: a private well is not supplied by a water utility, so there is no utility report to read, and well owners are usually responsible for testing their own water. A certified testing laboratory can tell you what is worth looking at, and the system should be chosen with those results in hand rather than guessed from a product page.
Questions to ask yourself first
- Do I own my home or rent it? Anything that changes the plumbing may need a landlord's permission or a plumber.
- What do I want from the water: everyday drinking water (browse Everyday drinking water), showers (Showers & bathing), or the whole house?
- How much water does my household drink and cook with each day? One person and a family of five are very different cases.
- How much space can I give: a shelf, a counter, a cabinet or a utility room?
- Who will change the cartridges, and will they remember? Our guide to when to change a water filter covers schedules and habits.
- Does my water come from a utility or from a private well?
- Is the exact model certified for the claims I care about? How to read a water filter label explains how to check.
Before you install anything
Installation instructions come first, whatever you choose. For anything connected to your plumbing, turn off the water supply, release the pressure as the instructions describe and follow the maker's steps in order. If you are unsure at any point, ask a licensed plumber, and remember that local plumbing rules can apply to some work.
If your question is about your water
A product page can tell you how a filter is installed and what it has been tested for. It cannot tell you whether your water is right for you. If you have a health concern, a medical condition or a question about water safety, contact your local water utility (most publish an annual water quality report), a certified testing laboratory or a health professional.