Complete Guide to Under-sink Reverse Osmosis Filters


Complete Guide to Under-sink Reverse Osmosis Filters

Do you want to make sure your drinking water is clean and healthy? If so, an under-sink reverse osmosis filter system may be exactly what you need.

RO can remove a wide range of contaminants – lead, heavy metals, fluoride, chromium 6, pesticides and herbicides, chlorine, and a lot more. It also reduces minerals such as calcium which can build up inside plumbing over time causing blockages or reduced flow rates.

If you’re looking for an under-sink RO system that will provide clean drinking water for your family at an affordable price, then this guide is exactly what you need! We have all the information about these systems so you can make an informed decision on whether it’s right for your home or not!

In this article, we will cover how to choose a reverse osmosis system that best suits your needs so you can have fresh drinking water at all times!

What is Reverse Osmosiswhat is reverse osmosis

Reverse osmosis is a water filtration process that uses pressure to force water through a semi-permeable membrane. The membrane acts as a filter, allowing pure water to pass through and trapping contaminants.

This process removes up to 99% of the dissolved solids in your tap water, including lead and other heavy metals, chlorine (which can cause unpleasant odors), nitrates/nitrites, arsenic, fluoride, chromium 6+ (the carcinogen made infamous by Erin Brockovich), pesticides and herbicides. It also reduces minerals such as calcium which can build up inside plumbing over time causing blockages or reduced flow rates.

How reverse osmosis works

The heart of the reverse osmosis system is the membrane. The RO membrane is a porous plastic sheet that has thousands of tiny holes in it called pores. The diameter of the pores is extremely small – the most common pore size is 0.0001 microns. This tiny opening in the membrane allows pressurized water to pass through while the larger contaminants are retained or filtered out.

The size of the pores is carefully determined during the design process to match the contaminants being targeted. If the holes in the membrane are too large, then the contaminant can pass through and the filter won’t work. If the holes are too small, then the membrane will become clogged with particles sooner than it should – this results in a reduced filter life and higher costs to replace the filters.

Types of RO systems

Reverse osmosis systems come in a variety of sizes and configurations. The type you choose will depend on your specific needs and the water quality entering into the system.

The main difference is they are designed for different flow rates and volume of water to be treated. They can be designed to treat all of the water that comes into your house or just the water your drink and cook with.

under sink RO filter system
Under-sink RO filter systems are the most common type installed in the US.

The most common size configurations are:

  1. whole house: a whole house RO system is designed to treat all of the water that enters your house. It’s usually installed at the point where the main water line enters your home. This configuration is also known as point-of-entry (POE) filtration.
  2. under-sink: an under-sink system, also known as a point-of-use (POU) unit, is designed to treat only the water you drink and cook with. These systems are typically installed under the kitchen sink or in another
  3. countertop: a countertop system is designed to sit on top of the counter and treat only the water you drink and cook with.
  4. portable: a portable RO system is designed to be taken with you when you travel or move.

Why choose an under-sink reverse osmosis system

An under-sink RO filter is the best option for most people because it’s the most convenient and affordable way to get clean drinking water.

This configuration only treats the water you will be drinking and cooking with. In most cases this is the right choice. For example, if you are removing lead, then you want to be sure the water you drink and cook with is safe. You don’t need lead-free water to flush toilets or shower.

An under-sink system is installed under the kitchen sink and provides clean water where you use it most. It’s also out of sight, so it doesn’t take away from your decor.

On the other hand, if you have an odor problem, then a whole house system may be the best solution.

A countertop RO filter system is a good choice if you don’t have space under your sink or if you are a renter and you aren’t allowed to make changes to the plumbing.

Here’s an RO system you may be interested in

This is the under-sink reverse osmosis system I recently installed in my kitchen. I chose it because it was reasonably priced and seemed easy to install. I like it because it’s very easy to maintain, and it removes all of the contaminants I’m worried about – lead and PFAS.

Check Pricing on Amazon

Benefits of Reverse Osmosis

Reverse osmosis is a very effective way to remove contaminants from your tap water. If the impurities you’re looking to remove harm your health – lead, heavy metals, chromium 6, PFAS, pesticides, herbicides – then the benefit of having an RO system are obvious.

But are there other benefits of installing a reverse osmosis system in your home?

Here are just some of the benefits you can expect:

  1. Clean, fresh tasting water for drinking and cooking
  2. No more unpleasant tastes or odors caused by chlorine or other chemicals
  3. Reduced exposure to harmful chemicals and contaminants
  4. Cleaner dishes – no scale or deposits because all minerals are removed
  5. Reduced mineral build-up inside of your plumbing, appliances and fixtures which can cause reduced flow rates or blockages over time
  6. Peace of mind knowing your drinking clean, safe water

Having an RO system eliminates the need to purchase bottled water. This represents a big cost savings and reduces your impact on the environment.

Disadvantages of Reverse Osmosis

Reverse osmosis is a great way to remove impurities from your drinking water. But there are some drawbacks to having an RO filter.

  1. Maintenance: RO filters also require regular maintenance in order to keep them working properly. This includes replacing the prefilters and membrane on a regular basis – typically every 3 to 6 months depending on the water quality and your usage.
  2. Ongoing costs: RO filters also tend to be more expensive than some of the other methods available – like activated carbon filters.
  3. Water waste: The reverse osmosis process wastes a lot of water. A typical under-sink RO system wastes between 1 and 4 gallons of water for every gallon of purified water it makes.
  4. Space: The filter system takes up a significant amount of space under your sink.
  5. Loss of treatment performance: If you don’t keep up with the maintenance – like changing the sediment and carbon filters routinely – you risk damaging the RO membrane. If the membrane is degraded, then contaminants “breakthrough” and you lose the ability to effectively treat your water.
  6. Low water flow rate: The production rate of under-sink RO filters is very low. Most people complain that the water trickles out of the faucet. You can overcome this problem by purchasing a system with a storage tank which allows you to quickly fill a pot of water for cooking or making coffee.

Features to Consider for Your RO System

Before you purchase an under-sink RO system, you should educate yourself about all of the features and options that are available. A little bit of research can go a long way in ensuring that you get the best system for your needs and budget.

Here are some of the features to consider:

  1. Particle filter: A good under-sink RO filter will include a particle filter to remove rust, dirt, and scale from the water before it can foul the membrane filter. These filters improve the performance of your system and extend the life of the critical RO membrane.
  2. Carbon adsorption filter: Chlorine and solvents in your water can degrade and damage the RO membrane. Carbon filters remove these compounds from the water, extending the life of your RO membrane.
  3. Post-carbon filter: A post-carbon filter is used to remove any tastes and odors that may be left after the RO process.
  4. Storage tank: RO filters produce water at a rate that is much lower than your faucet does. A storage tank allows you to store a reserve of purified water so that you have enough for cooking or drinking without waiting for the water to trickle out of the faucet.
  5. Remineralization: RO removes more than just contaminants from your water. Beneficial minerals that taste good and are good for your health are also filtered out. If you want to replace some of these minerals, you need a remineralization filter. This unit adds calcium and magnesium to your water to improve the taste and quality of your water.
  6. Ultraviolet light disinfection: Although reverse osmosis removes bacteria and viruses, in some instances you can still have microorganisms in your treated water. If you are concerned about this risk, you can add an ultraviolet light disinfection system to kill any microorganisms that may be present in your water.
  7. Booster pump: If your water pressure is low (less than 40 psi), you will need a booster pump to increase the water pressure so that the RO system can function properly. Even if you have adequate water pressure, a booster pump will improve the performance and production rate of your RO system.
  8. Automatic shut-off valve: Occasionally fittings and hoses come loose on an RO system, which can cause water to leak onto the floor. An automatic shut-off valve senses when a leak has occurred and shuts off the water supply to the filter, preventing any further damage.

By considering all of these features, you can be sure to select the best under-sink RO system for your needs. With a little bit of research and comparison shopping, you can ensure that your new system will serve you well for many years.

Learn more about remineralization by reading my article.

How Much Does Under-Sink RO System Cost

Under-sink reverse osmosis filters are available in a wide range of prices and sizes. This also means that the level of quality and features the filter comes with can vary greatly.

To get a good idea of what to expect to pay, take a look at the prices below for some popular models on the market today:

  • Bare bones system: include sediment and carbon filters, no tank. Costs between $110 and $200.
  • Middle-of-the-road system: includes sediment, carbon, post-carbon filter, and storage tank. Costs between $150 and $310.
  • Premium system: includes sediment, carbon, post-carbon filter, remineralizer, and storage tank. Costs between $280 and $500+.

The cost of an under-sink RO filter will vary depending on the features that are included in the unit. A basic system with a particle filter and carbon adsorption filter typically costs around $200. If you want additional filters, you can expect to pay more for your system.

Many under-sink RO systems come with a storage tank, but not all do. Adding a tank might cost an additional $30 to $95.

A UV light disinfection unit will add $120 to $300 to the cost of your filter.

If you are looking at a unit that includes all of the features mentioned above, be prepared to spend closer to $500 or even up to around $800 for an advanced RO system. Be sure to shop around and compare prices before making any decisions about which model is best for you.

If you are on a tight budget, there are some lower-priced models available that still offer many of the features you need. However, be aware that you may have to make some compromises in terms of quality or performance.

Maintenance and Operation of Reverse Osmosis Filters

It is important to remember that an under-sink RO system will require regular maintenance in order to keep it running at its best. This includes changing the filters on a regular basis and cleaning the unit periodically.

The frequency with which you will need to change the filters depends on the type of filter that is used in your system. For example, if you have a sediment filter, it will need to be replaced every 3 to 6 months. A carbon filter typically needs to be changed every 6 to 12 months.

The RO membrane can last for many years if you replace the sediment and carbon filters regularly. If you fail to do this, the membrane could become damaged and need to be replaced. Most manufacturers recommend replace the membrane every 12 to 24 months.

If your system does not come with a storage tank, it is best to leave an empty container under your sink as a place for collected water. Be sure that there are no kinks in the line so that any filtered water can easily flow into the reservoir

Cleaning the RO unit is also important for keeping it running smoothly. I clean my system once a year to remove any scale or particles that accumulate in the tubing and tank. I also sanitize the storage tank to prevent any bacteria growth.

Regularly cleaning the unit also keeps you aware of how it is operating and if there are any problems that need to be addressed. If your system has a sediment filter, make sure that the water flowing through it does not appear cloudy or discolored after filtration. This can indicate an issue with the filter, and it will need to be replaced.

If you notice a decrease in water flow or an increase in water pressure, this is another sign that there is a problem with your system that needs to be addressed.

Be sure to consult the owner’s manual that comes with your RO filter for more specific instructions on how to maintain your system.

Installation of Under-sink RO System

Once you’ve determined all of the features and options you need, it’s time to install your under-sink reverse osmosis system.

Many RO systems are designed for easy installation, and some can be installed with very few tools or plumbing knowledge needed. However, there are some important planning and design steps that you need to complete before purchasing an RO filter.

Professional installation
A well-planned layout will result in a professional looking and efficient installation.

Planning is critical

Reverse osmosis filters need a minimum water pressure (35 to 80 psi) in order to function properly. If your water pressure is below this level, you will need a booster pump to increase the pressure or you may need to consider a different type of filter. You can measure your water pressure with a pressure gauge connected to a hose bib or your sink.

Your filter system will take up space under you sink. Measure the cabinet and compare it to the dimensions of the RO filter. Give yourself room to install the system and plenty of elbow room to replace the filters. You’ll be surprised how difficult it is to change a filter if you can’t get your upper body into the cabinet under your sink.

Plumbing connections and other considerations

Be sure to read and follow the manufacturer’s instructions carefully – you don’t want to damage your new filter system or create a plumbing disaster.

RO filters also require access to incoming cold water and a place to discharge the waste water. Since you’re installing an under-sink filter, you have access to both of these.

Confirm the type of pipes you have and the connection fitting that comes with the filter system. You may need to install an adapter or converter if the connection fits are different than what you have.

The waste water output can be sent directly down your drain, but most filters also include a tube that allows you to route the waste water into a nearby sink for disposal. Check to see what your filter requires.

You may need an air gap fitting to prevent backflow of contaminated water into your home’s potable water supply. An air gap is a U-shaped fitting that is installed on the discharge side of the RO filter and creates a physical separation between the potable and non-potable water supplies. This is a plumbing code requirement in some municipalities – check with your city or town to see what’s necessary.

Drilling holes in your sink or countertopRO filter faucet

The purified water from the RO filter is delivered through a dedicated faucet. You’ll need to drill a hole in your sink or countertop to accommodate the faucet.

If you need to drill in your countertop, be sure there is no electrical wiring or plumbing behind where you plan to make your cutout. Drilling through porcelain sinks requires extreme care and caution since it can easily chip or break the sink.

If you’re not comfortable drilling holes in your countertop or sink, many RO filter systems include a faucet that can be mounted on the edge of the sink. You can also hire a professional to do the installation for you.

Certification and Third-Party Testing

In the United States, there are not regulations or government requirements that address reverse osmosis system (other than general plumbing codes). Fortunately, man manufacturers choose to pursue voluntary certifications of their systems in order to verify the safety of their products and validate their claims.

The third-party agencies that manufacturers and water treatment professionals turn to are NSF and ANSI. NSF

Point-of-use reverse osmosis systems and components are covered by NSF/ANSI 58.

Certification to NSF/ANSI 58 indicates that the RO filter has been tested and the consumer can be confident that:

  • Claims about contaminant reduction are accurate
  • Nothing harmful is added to the water from the equipment (e.g., lead)
  • The equipment is rugged enough for its intended purpose
  • The manufacturer’s claims are accurate

Final Take on Under-Sink Reverse Osmosis Filters

There are many benefits to installing an under-sink reverse osmosis filter in your home. The RO process works by pushing the water through a membrane that only allows pure water to pass through while removing impurities. An RO system will reduce the amount of salt and minerals that enter your water, making it taste better. They also remove harmful contaminants like lead, heavy metals, and PFAS.

This blog post has given you all of the information you need about installing an under-sink reverse osmosis system in your home – from planning for installation costs to maintenance requirements. If you’re ready to install one today, we’ve got everything you need right here!

Chief Guru

Richard Boch is a chemical engineer responsible for designing water filtration systems for industrial and residential customers. He has more than 20 years of experience with ion exchange, activated carbon, and reverse osmosis. Richard's expertise has made him a go-to source for municipalities and businesses looking to improve their water quality. When he's not working, Richard enjoys spending time with his wife and two young children. You can also follow him on Twitter

Recent Posts