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A Guide to Under Sink Water Filtration Systems


When you’re paying attention to your water quality, you may notice questions starting to pop up everywhere. Is that odor coming from the sink itself or the sink water? Could the little particles I’m seeing be the first hint of a bigger problem? Is this drinking water safe?

The unfortunate truth is that you often can’t answer all these questions on your own. Many water quality issues can’t be detected by taste, sight or smell, leaving you to wonder what you’re really getting in every glass of drinking water. 

Luckily, you don’t have to settle for wondering — or worrying. There are various solutions at your disposal, like installing an under-sink water filter, and it all begins with a water test.

Let’s take a closer look at the water filtration process and find out how it can help you feel confident about every sip.


The First Step in Water Filtration: The Water Test

It’s easy to tell yourself you’d be able to notice any issues with your water quality. After all, you drink sink water every day — surely you’d notice a new odor or strange color.

types of water filtration systems

However, the truth is that water quality issues can be far more complicated — and more difficult to identify — than you might expect. That’s because a single element, like discoloration in your tap water, could be caused by different problems from a variety of sources. Further, some issues are purely aesthetic, while others could potentially impact your health, the longevity of your water-using appliances or even the structure of your home’s plumbing. Finally, the fact is that many serious water problems aren’t even observable.

Simply put, if you’re unable to identify exactly what’s happening when you turn on the sink, you’re essentially relying on guesswork to protect your home, water quality and even your family’s health. That’s why a water test is an important tool to have up your sleeve.

Everything You Need To Know About Water Testing

Water tests can and should be performed on both city and private well water systems. It’s recommended to have these tests once a year or whenever specific events occur, like floods, droughts or work performed on your home’s plumbing or well. You should also reach out to water experts for a test if you notice a change in your water quality — for example, new incidences of staining or a different odor.

Having a water test performed can help identify whether your drinking water is safe for long-term consumption. These tests can also tell you the specific cause or causes of observable water issues like:

  • Discoloration
  • Odors
  • Reduced appliance efficiency
  • Limescale buildup
  • Spotty dishes
  • Issues like dry skin or brittle hair

While it’s helpful to have this information, as well as other tested measurements like water hardness or water pH levels, a water test can tell you even more. Once you have your results, you’ll also be able to identify what your next steps should be. For example, if high levels of water hardness are causing limescale buildup, your water test can help you choose the best water softener for your needs.

Often, the results of these tests indicate that your water quality would benefit from a water filtration system. However, that can mean a lot of things, as there are all kinds of variables when it comes to water filters — so it’s smart to know what your options are.

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How Many Water Filter Types Are There?

The pursuit of water quality solutions is nothing new. It’s led to the creation of rules like the Guidelines for Canadian Drinking Water Quality and the Environmental Protection Agency’s Drinking Water Regulations. Closer to your home, this pursuit has also inspired the creation of multiple water filter types and filtration system options.

Here’s what you have to choose from when it comes to water treatment options:

Whole-Home Water Filtration Systems

A whole-home water filter is installed where your water source enters your home underneath your house. In this way, it can address all the water you use — which means you’ll have filtered water no matter where you turn on the tap. 

Whole-home filters are generally recommended for specific water quality issues like sulfur, iron, sediment and chlorine. That’s because these issues tend to impact more than just your drinking water, potentially creating concerns when using the affected water for cleaning and bathing as well. 

Sink Water Filtration Systems

Sink water filtration systems come in various types. This includes any filter mounted on the sink faucet itself; these systems tend to be simpler and less comprehensive than other sink water filter options.

For better, more complete filtration, you may want to explore under-sink filtration systems. As their name suggests, these are installed directly under your sink and only filter water for that specific tap. However, not all under-sink water filters work in exactly the same way.

To address taste, odor or appearance issues as well as specific contaminants like heavy metals and lead, it’s best to consider reverse osmosis under-sink systems.* Reverse osmosis creates a more robust, comprehensive filtration process, allowing you to trust that you’re getting cleaner water every time you turn on the tap. (While reverse osmosis systems are commonly installed under the sink, they also can be installed in utility rooms or basements, still providing filtered water from your kitchen sink but not taking up space under your counter.)

Countertop Water Filter Systems

If you’ve ever seen a filtered water pitcher, you’re already familiar with most of what countertop water filters and related products have to offer.  Simple and often less reliable than their more intricate counterparts, these filters aren’t really systems; rather, they offer a highly simplified process that filters drinking water as you pour. 

Most users find countertop water filters to be the least efficient sink water filter system. While they may be inexpensive and easy to use, these pitchers can also be wearisome to use for large amounts of water, like those needed for cooking or making large servings of a favorite drink.

Built-in Water Filtration Systems

Some water filter options are built right into your appliances — for example, your refrigerator. Like countertop water filter pitchers, these tend to be less comprehensive and can’t always provide the same level of reliability as other filtration system options.

With so many tap water filter types available, it can quickly become overwhelming to choose the best option for your current and future needs. Remember, though, you don’t have to rely on guesswork — a water test can help guide you in the right direction.


An Inside Look at Reverse Osmosis

One of the most important elements of any water filter is being able to understand how it works. If you don’t know what the filter is doing or how it keeps its promise to provide cleaner, safer drinking water, you might start to wonder if you can really trust it. The last thing you want to do is question every sip you take.

That’s why it’s helpful to brush up on one particular type of filtration — reverse osmosis (RO) — and find out why this approach makes some under-sink water filters so efficient. 

What is Osmosis?

An RO system is based on the natural process of osmosis, which is vital for living things. 

Osmosis describes the movement of water across a semipermeable membrane — often the plasma of a cell. This membrane allows the water to travel through but blocks other substances, creating cleaner water on one side and a high concentration of other substances on the opposite side. 

But what causes the water to move in the first place? That all comes down to the concentration of water molecules. Think of it like this: Osmosis is the process of creating equilibrium, which is what happens when there’s too much water on one side of a membrane and not enough on the other side. 

One example of osmosis occurs when you water your plants. If there are more water molecules in the soil than in the plant cell, osmosis occurs to create equilibrium. As a result, your plants stand up straight and look healthy.

When you under-water your plants, however, the soil dries out and it’s the plant cells that have the higher concentration of water molecules. Osmosis is triggered — but this time, water is leaving your plant and seeping into the dirt to create that equilibrium, and you’ll start to notice a wilting stem.

What is Reverse Osmosis (RO)?

Reverse osmosis is similar to osmosis, but there’s one important difference: The former is an artificial process and the latter is natural. That’s because osmosis is triggered by an imbalance of water molecules, which can be caused by something as simple as under-watering your plants; meanwhile, reverse osmosis occurs when water is purposely forced against a membrane at high pressure. 

Further, the membranes involved in osmosis are generally biological, while those in reverse osmosis are synthetic. That’s good news for you, because it means you don’t have to worry about under-sink water filtration systems using cell plasma.  

How Does a Reverse Osmosis System Work?

When a sink water filter works via reverse osmosis, filtration generally occurs in four stages:

  1. First, water flows through an initial filter. This is where the presence of larger sediment, like sand or dirt, is greatly reduced.
  2. Next, the water travels through an activated carbon filter. In this stage, issues such as unpleasant tastes and odors caused by excess chlorine are addressed.
  3. After that, water is forced against a semipermeable membrane at high pressure. This membrane is woven so tightly that many contaminants — even those as small as a single atom — are blocked.
  4. Finally, once the reverse osmosis treatment is complete, your drinking water passes through optional additional filters. Depending on the system, these filters can enhance taste, alter water’s pH levels and more.

This process occurs automatically, which means you can turn on your tap anytime and enjoy a virtually unlimited supply of filtered water from your sink.

View All Culligan RO Systems


Sink Water Filtration: Frequently Asked Questions

Even once you’ve brushed up on all the different water quality solutions, learned how a sink water filter works and explored the basics of reverse osmosis, there’s more to learn about sink water filtration systems. Here are a few frequently asked questions:

Does Filtered Water Have a Taste?

Filtered water has a taste — but exactly what taste will depend on several factors.

For example, if your filtration system removes certain minerals, your water may taste different than what you’re accustomed to. That’s why some people prefer under-sink systems that can add minerals back into the water after the reverse osmosis process.

It’s also important to replace filters when necessary and recommended. As these filters do their job, they can become worn out or less effective, which can lead to unfamiliar tastes. 

Regardless, if taste issues persist, remember to have a water test performed to make sure you know what’s really going on with your water supply.

Do Sink Water Filtration Systems Make Noise?

Because an under-sink filter is installed indoors instead of underneath your home, you likely want to know whether you’ll hear the system doing its job. 

The good news is that, if installed and functioning properly, most sink water filtration is quiet. When the system is first installed, you may notice slight sputtering or gurgling noises as the pressure balances out; this is normal and will eventually stop.

However, if your system continues to make noise or begins making new sounds, you may want to call your installer. This could be a sign that something isn’t working quite right. 

Can You Have a Sink Water Filter and a Water Softener?

Yes. Under-sink water filtration systems and water softeners do different jobs in your home. The former addresses drinking water quality, while the latter helps solve hard-water problems such as limescale buildup around showers and faucets, spotty dishes and even dry skin. That means the systems can work together to create a comprehensive solution to your water quality problems, putting you firmly in control of cleaning, bathing, cooking and drinking water.

Do Sink Water Filters Work For Well Water?

Yes. Municipal and well water supplies don’t always have the same problems. For example, hard water is a particularly common issue for well water users, while chlorine taste is a more frequent complaint among those using the city water supply.

The good news is that a sink water filter can help reduce contaminants and improve water quality no matter where your water comes from. It’s still important to start with a water test so you know if additional solutions, like a water softener, might be necessary — but you can count on an under-sink system to help improve your well water experience. 

Does a Sink Water Filtration System Impact Water Pressure?

If you’ve ever had to scrub particularly stubborn food off your dishes before putting them in the dishwasher, you know how important it is to have good water pressure at the kitchen sink. In fact, water pressure is important for every tap in your home — which means you shouldn’t have to compromise on this element just to have cleaner, safer water.

When installed properly, an under-sink water filter shouldn’t impact your water flow. If you notice any issues, don’t assume these are a normal part of the system; instead, call your installer to double-check the filter and connections.

Are Sink Water Filters Environmentally Friendly?

Are you looking for a way to make your everyday life a little bit greener? Under-sink water filtration is a great place to start. By providing a virtually unlimited source of filtered water for your home, this approach reduces the need for wasteful single-use water bottles. In fact, thanks to Culligan® water filtration solutions, 15 billion plastic bottles are saved from global landfills each year. Culligan’s Aquasential® Smart Reverse Osmosis and Aquasential® Reverse Osmosis systems are also the world’s most efficient reverse osmosis drinking water filtration systems.**


Find Your Ideal Filtration System

As soon as you start paying attention to your water quality, all kinds of questions can pop up — but luckily, you never have to be without answers. A water test can help you identify the cause of any problems and direct you toward solutions like water softeners and under-sink water filters. From there, the choice is up to you — what kind of sink water filter best suits your needs?

If you’re not sure how to answer this question, you’ve come to the right place. Our Culligan experts are always happy to help you find your ideal filtration solution, from an RO system to a whole-home water filter.

Take the first step today by scheduling your free, in-home water test.



*Contaminants may not be present in your water.
**Efficiency is based on 3rd party testing to NSF standards

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