A point-of-use reverse osmosis (RO) system is a water filtration device that is connected to a single fixture (e.g., under the kitchen sink) and uses the process of RO to remove contaminants from the water supplied to that fixture. RO is the process by which pressure forces water through a semi-permeable membrane, creating a stream of treated water, called “permeate,” and a stream of reject water called “concentrate” or “brine.” These systems can potentially remove water contaminants such as lead, volatile organic compounds (VOCs), PFAS, arsenic, bacteria, and viruses. Point-of-use RO systems are typically installed in residential settings but can also be found in commercial office spaces or kitchens.
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Treat With Efficiency
While RO systems can improve water quality, these systems can also generate a significant amount of water waste to operate. For example, a typical point-of-use RO system will generate five gallons or more of reject water for every gallon of treated water produced. Some inefficient units will generate up to 10 gallons of reject water for every gallon of treated water produced. In contrast, point-of-use RO systems that earn the WaterSense label must demonstrate that they send just 2.3 gallons of water or less down the drain for every gallon of treated water they produce.
All products bearing the WaterSense label are independently certified to ensure they meet EPA criteria for efficiency and performance. The WaterSense specification for point-of-use RO systems ensures that labeled RO systems are just as effective at providing the high-quality treated water consumers expect from these products. For more information on RO systems, including how they work and how to select an RO system that is right for you, view this WaterSense report, Treating Water With Less Waste (pdf) .
While the water provided by public water suppliers in the United States is some of the safest in the world, there are times when consumers may want to employ additional treatment technology to ensure safety of well water or publicly-supplied water. Due to the water-intensive nature of RO, WaterSense does not intend to promote the installation of RO systems for all applications or encourage their use over other water treatment technologies that do not waste as much water (e.g., filtration systems). In some cases, other treatment methods that use little or no water, such as filtration, are sufficient to meet consumer treatment needs. For more information, read the WaterSense Guide to Selecting Water Treatment Systems (pdf).
WaterSense Savings
For consumers who are planning to replace their reverse osmosis system at the point of water use, selecting a WaterSense labeled model will reduce water use on average by more than 3,100 gallons of water per year compared to the water usage of a typical point-of-use RO system. This translates to a savings of 47,000 gallons over the lifetime of the system.
If all point-of-use RO systems sold in the United States were WaterSense labeled, we could save more than 3.1 billion gallons of water across the country annually, which is equivalent to the annual household water needs of nearly 41,000 American homes.
Read the Point-of-Use Reverse Osmosis Systems fact sheet (pdf) for more information.
Performance
As part of the WaterSense specification development process, EPA examined key performance metrics to ensure consumer satisfaction. EPA also considered the impact of reducing water waste on RO system performance.
All WaterSense labeled point-of-use RO systems are independently certified to meet performance criteria to ensure user satisfaction and health and safety. Performance criteria address the following areas:
See the Performance Overview for more information on how WaterSense assessed performance when developing the specification.
Specification
In November , EPA released the WaterSense Specification for Point-of-Use Reverse Osmosis Systems.
EPA hosted a meeting for manufacturers to discuss the final specification and process for earning the WaterSense label for RO systems on December 17, . The presentation and recording are available below.
For more information about the specification development process for point-of-use RO systems, including the draft specification, public response to the draft specification, and EPA’s response to public comments, please visit the Specification for Point-of-Use Reverse Osmosis Systems Background Materials Page.
US Water Systems is one of the premier manufacturers of Reverse Osmosis Systems, which are engineered for higher recovery rates, minimum energy consumption, continuous commercial duty, simplified maintenance, and user-friendly operation. US Water Systems’ RO Systems have all of their components located for easy access and inspection. All US Water Systems’ commercial-grade RO systems come with a built-in booster pump and the longest warranty in the industry.
Reverse Osmosis is the best available technology for "full spectrum" water purification from organic contamination and inorganic contamination such as toxic metals, salts, toxic substances (such as nitrates, metallic salts, and cyanides), as well as all kinds of particulates, asbestos, PCBs, pesticides, herbicides, drug metabolites, pharmaceuticals in drinking water, and even microorganisms. Ultraviolet Disinfection is always recommended, especially if you have a problem with microorganisms.
Carbon filtration alone does not remove inorganic contamination (when present) effectively, which is where Reverse Osmosis excels. On the other hand, Reverse Osmosis is a much more "hands-on" technology compared to carbon filtration and requires that you take a close look at your water chemistry to see if you have any water quality issues that will foul the RO Membrane. Reverse Osmosis also requires a certain amount of water pressure in order to work properly.
The rule of thumb for the pressure and volume required is 60 psi inlet pressure. Then, the system gallons per day rating (gpd) should be doubled to ensure coverage for makeup water and drain water. If you have less than that, you risk shutting off the RO systems with pressure faults.
“PF,” or Pressure Fault, is one of the main technical support calls we get. This is typically because someone didn’t check their peak sustained flow. This is not fatal, as booster pumps, pressurizers, ballast tanks, and larger lines can be added, but it is best to consider this in the beginning.
Reverse osmosis (RO) removes the widest spectrum of contaminants of any water treatment process. Reverse osmosis is highly effective at removing a wide range of contaminants from water. It works by forcing water through a semipermeable membrane that blocks larger molecules and impurities. Here are the primary contaminants that RO systems remove:
Heavy metals: Lead, mercury, arsenic, cadmium, chromium.
Salts & minerals: Sodium, chloride, fluoride, nitrates, sulfates.
Radioactive contaminants: Radium, uranium.
Pesticides & herbicides: Glyphosate, atrazine, chlorpyrifos.
Pharmaceuticals: Antibiotics, hormones, pain relievers.
Industrial chemicals: Volatile organic compounds (VOCs), benzene, toluene.
Bacteria: E. coli, Salmonella, Cholera.
Viruses: Hepatitis A, Norovirus, Rotavirus.
Protozoa & Parasites: Giardia, Cryptosporidium.
Chlorine & Chloramines (if pre-filtered with activated carbon)
Sediments & Rust
PFAS ("Forever Chemicals")
Bad taste & odors
However, RO does not remove some dissolved gases like carbon dioxide and some volatile organic compounds (VOCs) unless paired with an activated carbon filter. Some beneficial minerals like calcium and magnesium are also removed, so remineralization filters may be needed.
There is a misconception that because reverse osmosis removes such a wide spectrum of contaminants, it can be hooked up to any water supply and it will instantly purify that water. Nothing could be further from the truth!
A reverse osmosis system produces water much more slowly than a filter or a water softener. RO Systems are rated in how many gallons a day they can make. As an example, if a RO system is rated at 4,000 gpg, it will produce approximately 2.77 gpm (divide the gpd by the number of minutes in a day, which is 1,440). Please note that all reputable commercial reverse osmosis manufacturers rate every RO system by how many gallons per day (gpd) it will produce. In order to be able to compare and rate each system properly, they are all rated under the same factors or parameters.
Feed water pressure: Higher pressure improves flow rate.
Water temperature: Standard ratings assume 77°F (25°C); colder water reduces output by up to 2% per degree.
Total Dissolved Solids (TDS): Higher TDS reduces efficiency.
Membrane fouling: Dirty or clogged membranes lower performance.
For best operation, the water needs to be relatively “clean,” meaning that it should be free of hardness, chlorine, and a number of other substances like iron and manganese. It is the purchaser's responsibility to ensure that their feedwater falls within the values of these required parameters before purchasing a system. Feedwater outside the stated parameters will require one to add additional pre-treatment.
Maximum Hardness: <1.0 Grains Per Gallon
Maximum TDS: ppm
Chlorine Tolerance: < 0.1 ppm, but ZERO is best
Oxidizer Tolerance: ZERO
Maximum Hydrogen Sulfide: 0 ppm
Maximum Iron: 0.5 ppm, but ZERO is best
Maximum Manganese (Mn): 0.05 ppm
Maximum Silica: < 1 ppm
[Barium or Strontium] + Sulfate (SO4): is detrimental to Reverse Osmosis Membranes. Use a water softener to remove these when both are present.
Maximum Feedwater Turbidity: 1 NTU
Pre-treatment is required if any of the above values are exceeded or your system will be damaged.
Minimum Feed Pressure: 35 PSI
Nominal NaCl % Rejection: 98.5%
Minimum NaCl % Rejection: 96%
Typical Operating Pressure: 150 PSI standard. Approx. 100 PSI with Low Energy Membranes
pH Range Continuous Operation: 3-11
Maximum Temperature: 105° F.
Minimum Concentrate Flow Rate: 5:1
Protect units from freezing temperatures.
Permeate flow and salt rejection is based on the following test conditions: 550 PPM TDS treated tap water, 150 PSI, 77° F., pH:7
NOTE: Permeate Flow (Gallons Produced Per Day) may vary + or- 15% with each membrane and also varies according to water temperature. Colder water slows down the membrane performance but not water quality. It is the purchaser's responsibility to ensure that the water temperature will be high enough to deliver the desired quantity.
In the past, every RO system had a water softener before it, but with the advent of modern anti-scalants, water softeners are no longer required. In fact, it is arguably true that chemical anti-scalants are more effective than a water softener. For example, the Waterlogix Hyper-Guard Plus is a powerful anti-scalant, specially formulated for feedwaters with high levels of metal oxides, silica, and scale-forming minerals.
Controlling the precipitation of certain cations or salts has long been an issue with making Reverse Osmosis (RO) technology economically viable. Scale precipitates on the membrane surfaces, causing the permeate flow and quality to be adversely affected. Excessive build-up on the membrane can permanently damage it and accelerate the need for replacement.
RO anti-scalants, sometimes called scale inhibitors, are special chemical formulations that are added to increase the solubility of soluble salts. The use of such anti-scalants can form an essential component in the operation of solidly engineered reverse osmosis systems. The Anti-Scalant is introduced right ahead of the RO Membranes with the use of an injection pump, such as the Stenner Pump pictured to the right.
In fact, most commercial RO systems now use anti-scalants over water softeners. So unless you think lifting salt bags is an Olympic Sport for which you are training, there is no need to even have heavy salt bags. A 32-ounce bottle of anti-scalant might last two to three months (depending upon your water usage), and a 5-gallon Pail might last over a year.
It is also vitally important that chlorine and/or chloramine be removed ahead of a reverse osmosis system, as the chlorine or chloramine will attack the membranes and degrade them rapidly. To effectively remove chloramine or chlorine, it is imperative that a carbon filter or catalytic carbon filter is sized correctly. In very large systems, chlorine can be removed with injection of a chemical.
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Chlorine must be removed before water enters a large RO system because it can degrade thin-film composite (TFC) membranes, causing irreversible damage. Here are the most effective methods for chlorine removal in high-capacity RO applications:
How It Works: Activated carbon absorbs chlorine through adsorption.
Best For: Medium to large RO systems (1,000–10,000+ GPD).
Typical Setup:
Large GAC tanks (10" × 54" or larger) for continuous dechlorination.
It can be installed before or after sediment filtration.
Flow rate sizing is critical to ensure enough contact time.
Pros:
Highly effective for both chlorine and chloramine removal (with catalytic carbon).
No chemical dosing is required.
Cons:
Requires periodic backwashing to maintain efficiency.
Carbon media needs replacement over time.
2. Catalytic Carbon Filters
How It Works: Similar to GAC but enhanced for faster chlorine and chloramine removal.
Best For: Large RO systems (5,000+ GPD) that need chloramine removal.
Pros:
Removes chlorine and chloramine.
Faster reaction time than regular carbon.
Cons:
More expensive than standard GAC.
How It Works: Sodium metabisulfite (SMBS) neutralizes chlorine before RO.
Best For: Industrial and municipal RO systems (50,000+ GPD).
Typical Setup:
SMBS dosing pump injects a precise amount of SMBS into feed water.
Requires a mixing tank for reaction time before RO membranes.
Pros:
Effective at high flow rates.
Works instantly.
Cons:
Requires chemical handling and dosing system.
Excess SMBS can lead to microbial growth in storage tanks.
How It Works: High-intensity UV light (185 nm wavelength) breaks down chlorine molecules.
Best For: Systems requiring chemical-free dichlorination.
Pros:
No chemical residue.
Works for high-flow applications.
Cons:
Less effective for chloramine.
Requires pre-filtration for optimal performance.
In commercial reverse osmosis (RO) systems,bladder tanks and atmospheric tanksserve as storage solutions for purified water, but they operate differently and are used in distinct applications. Here’s a breakdown of their differences:
Structure: A bladder tank consists of a pressurized vessel with an internal flexible bladder or diaphragm that separates water from an air pocket.
Operation: When water fills the bladder, it compresses the air, creating pressure. When water is needed, the air pressure pushes the stored water out, eliminating the need for an external booster pump in many cases.
Maintains consistent pressure, allowing direct delivery to faucets and systems without an external pump.
Compact and requires less space.
Reduces the risk of contamination as water remains enclosed.
Limited storage capacity (typically up to 100 gallons in commercial systems).
Decreased efficiency in high-demand applications. This is because the back pressure from the tank reduces the water quality being produced by the RO system. (Note: the highest water quality will ALWAYS come from a system with an atmospheric tank).
The bladder may degrade over time, requiring replacement.
Heterotrophic bacteria and slime can accumulate and grow inside a bladder tank so it will need to be cleaned periodically.
Structure: These are open or vented tanks, typically made of polyethylene or fiberglass, and do not have an internal bladder.
Operation: Water from the RO system fills the tank by gravity, and a separate booster pump is needed to distribute water at the required pressure.
Advantages:
It can store large volumes of water (hundreds to thousands of gallons).
Works well for high-demand applications and multiple distribution points.
Allows for additional treatment, such as re-pressurization, UV sterilization, or re-mineralization.
Delivers higher quality water.
Requires an external pump for water delivery.
Higher risk of contamination due to air exposure (requires proper venting and sanitation – typically requiring disinfection with UV or ozone).
Takes up more space compared to a bladder tank.
Use a bladder tank for smaller commercial applications where moderate storage (under 100 gallons) and consistent pressure are required without additional pumps. If using a bladder tank, remember that bacteria (heterotrophic) can build up inside and needs to be sanitized periodically. Additionally, a UV Disinfection system should be utilized after the bladder tank.
Use an atmospheric tank for larger applications, such as restaurants, manufacturing, and large-scale RO systems, where high storage capacity and flexibility in water distribution are needed.
How many gallons per day do you require? You should add about 20% to 30% to this number to account for variation and margin of error. Also, colder water will produce much fewer gallons per day than the stated production capacity, based on 77-degree water. You need to base the system size on the coldest water temperature your system will experience, such as the water temperature during winter.
To save electricity and reduce wear on the pumps and motors, it is recommended that you size the RO system so that the pump only has to run no more than 4-6 hours per day. This saves you money on electricity and motor replacements. While this is not necessary, it is highly recommended. A good rule of thumb is to figure out what your maximum daily capacity will be, add the 20% as a "fudge factor," and then 4X that number (so that the system only has to operate up to 6 hours per day).
Remember This: Reverse Osmosis Systems are rated at their respective gallons per day at 77 degrees F. If you live in a cold water climate where the water could be considerably below 77 degrees, you need to realize that you can lose approximately 2% production for every degree below 77 degrees F.
HOMEOWNERS: For whole house applications, each household occupant "typically" consumes 80-100 gallons per person per day, on average. So, four people will typically need about 400 gallons per day. Anticipate holidays and guests. Take into account swimming pools, hot tubs, or any additional water-consuming activities you may have. If your water is not so bad you may ask your installer to leave the garden hoses and swimming pool supply as Untreated (not RO purified). The National Average, according to the International Water Works Association, is 106 gallons per day.
You should always obtain a good water analysis of your water. You can obtain one from US Water Systems if you do not have one available. We offer two tests: The Basic Water Test and The Premium Water Test. This step is critical, do not buy any RO system unless you have at least a Basic Water Analysis.
Specifically, we need to know the following: Total Hardness, TDS, Iron, Sulfide, Manganese, pH, Chloride, Alkalinity, SDI (silt density index), Turbidity, Silica, Sulfate, and [Water Temperature during winter]. Barium and Strontium are also a serious problem when combined with Sulfates (SO4). Please inform us of any other water problems or special concerns that you know of, such as, high levels of TSS, Radon, or unsafe levels of any contaminants such as Arsenic. If you are treating unsafe drinking water, it is your responsibility to work with an on-site Water Treatment Specialist to ensure you are getting the proper results. Laboratory confirmation and periodic monitoring is a part of that. If you have high Chlorides and/or acidic water, you should upgrade the Titan's pump to stainless steel.
RO will typically lower your pH to some degree. You do not want acidic (pH < 6.9) RO water, especially with copper pipes. You may need to raise your water pH (after the RO system) to avoid leaching copper or metal pipes and faucets. This can be done simply by adding a calcite cartridge filter. There are also health concerns about long-term consumption of acidic water. US Water offers inexpensive, healthy solutions for that problem, such as a Calcite Mineral Tank or Calcite mixed with 50% Magnesium Oxide.
If you have water that is too hard, you will either have to install a water softener upstream of the RO system, or you may be able to install an Anti-Scalant Chemical Injection System upstream of the RO unit. If you have too much Iron, Sulfide, or Manganese, you will have to remove them with a well-designed Oxidation Unit placed upstream of the RO system.
Some companies are saying that their Commercial Reverse Osmosis Systems can make 5 gallons of water for every gallon wasted. Yeah, but not for long. In reality, if you have relatively clean water, you might get by at most 4 to 1, but you will never go wrong at 3:1. We have seen systems that only wasted 1 gallon for every 5 gallons made, but the membranes only lasted six weeks. Set at 3:1; the membranes will last for years.
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