The Water Research Center provides information on various drinking water treatment systems. This section focuses on the use of reverse osmosis to treat drinking water, well water, city water, rainwater, and tap water.
Reverse osmosis (RO) systems are frequently used to reduce the levels of total dissolved solids and suspended particles within water. These systems remove various ions, metals, and specific organic, inorganic, and bacterial contaminants. In general, the process of reverse osmosis can effectively remove high percentages of dissolved ions such as Arsenic, Antimony, Aluminum, Barium, Beryllium, Cadmium, Calcium, Chloride, Chromium, Copper, Fluoride, Iron, Lead, Magnesium, Manganese, Mercury, Nitrate, Potassium, Selenium, Silver, Sodium, Sulfate, Thallium, and Zinc; radionuclides like Radium and Uranium; select pesticides like Endrin, Heptachlor, Lindane, and Pentachlorophenol; and particles like cysts, oocysts, and asbestos fibers. Reverse Osmosis water treatment systems can remove PFAS from drinking water. “High-pressure membranes, such as nanofiltration or reverse osmosis, have been extremely effective at removing PFAS. (Source)
There are some contaminants not removed from water by RO systems. Reverse osmosis units do not effectively remove most organic compounds, bacterial microorganisms, chlorine by-products, or dissolved gases like carbon dioxide, methane, and radon. Therefore, it is necessary to address the presence of dissolved gases that may impact the water chemistry prior to the reverse osmosis process. The reverse osmosis process is not particularly effective at selecting specific anions or cations to remove from the water so there can be a tendency for reverse osmosis water to have a low pH and to be slightly more corrosive than the untreated water. This can be addressed by using a post-treatment remineralization filter. The RO membrane's efficiency in reducing the amount of contaminants in the water depends on the contaminant concentration, chemical properties of the contaminant, the membrane type and condition, and operating conditions. Reverse osmosis is considered an ultrafiltration process; it is also expensive.
The RO membrane alone may not be an effective method for total removal of these contaminants but a properly designed system may be effective in reducing these contaminants to safe levels. Contaminant removal by the system may vary depending on operating conditions and equipment. Reverse osmosis can significantly reduce the microorganism population in the water, but because these microbes may regrow on the membrane and cause the formation of bio-slimes or cause the membrane to prematurely fail, it is recommended that the water be properly disinfected prior to RO treatment. RO treatment systems have a few system components:
The RO treatment system requires pretreatment that most likely includes Particle Filtration, UV Disinfection, Chemical or Ion Exchange, and other pretreatment to prevent scale formation or bio-slime regrowth/growth. Because of all the pretreatment, these are typically point-of-use units and not whole-house treatment systems. RO Systems are commonly used when the water contains elevated levels of salts, such as chloride, Nitrate, Total Hardness, and Sodium.
Reverse osmosis unit performance is measured by a combination of the membrane rejection rate, see above, and the recovery rate for the system. The membrane rejection rate is the percentage of the contaminant that is not permitted to pass through the filter. The rejection rate can be used to predict the effectiveness of the treatment process and the feasibility of the approach. For example, if there were two water sources that required treatment and one water source (source A) had an arsenic level of 2000 ppb and the other source (source B) had a concentration of 50 ppb and the membrane had a 90 % rejection rate, then:
Source A 2000 ppb * 0.90 = 1800 ppb of the arsenic is captured and diverted to waste, but 200 ppb of arsenic would pass through the filter. This concentration exceeds the recommended USEPA drinking water standard of 10 ppb for arsenic.
Source B 50 ppb * 0.90 = 45 ppb of the arsenic is captured and diverted to waste, but 5 ppb of arsenic would pass through the filter. This concentration is below the USEPA drinking water standard of 10 ppb for arsenic, but would be at the drinking water limit for some states.
Recently, the recovery rates for reverse osmosis units have significantly increased by the addition of booster pumps and a permeate pump. The reverse osmosis booster pump increases the water pressure in the feed line, while the permeate pump does not increase pressure, but helps the reverse osmosis unit waste less water.
Notes:
Table 1 | Common Types of System Fouling (Cause and Approach)
We recommend that, prior to installing a Reverse Osmosis System, you Get Informed by gathering as much information as possible and Get Tested by conducting multiple levels of testing depending on your needs: Level 1 Observational Testing using our Self Test Web App, Level 2 Do-It-Yourself Testing, Level 3 Informational Lab Testing and, if needed, Level 4 Certified Testing conducted by a water professional.
If you have any questions please Contact the KnowYourH2O team.
Prior to implementing a treatment solution, we recommend the following tests:
<div class="product-note in-L6-bromate">Note: If the concentration is < 0.01 mg/L</div>
<div class="product-note in-L6-uranium">Note: Uranium less than < 0.030 mg/L</div>
<div class="product-note in-L6-benzene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-carbon-tetrachloride">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chloroform-trichloromethane">Note: If the concentration is < 0.080 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-ethylbenzene">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-methylene-chloride-dichloromethane-dcm">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-tetrachloroethylene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trichloroethylene">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-xylenes">Note: If the concentration is < 1 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-atrazine">Note: If the concentration is < 0.001 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-alachlor">Note: If the concentration is < 0.002 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-glyphosate">Note: If the concentration is < 0.7 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-2-4-d">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bis-2-ethylhexyl-phthalate">Note: If the concentration is < 0.006 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trihalomethanes">Note: If the concentration is < 0.08 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-haloacetic-acids">Note: If the concentration is < 0.06 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chlorite">Note: If the concentration is < 0.8 mg/L (POU Device System Component)</div>
The following are recommended Reverse Osmosis Treatment Systems:
<div class="product-note in-L6-bromate">Note: If the concentration is < 0.01 mg/L</div>
<div class="product-note in-L6-uranium">Note: Uranium less than < 0.030 mg/L</div>
<div class="product-note in-L6-benzene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-carbon-tetrachloride">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chloroform-trichloromethane">Note: If the concentration is < 0.080 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-ethylbenzene">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-methylene-chloride-dichloromethane-dcm">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-tetrachloroethylene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trichloroethylene">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-xylenes">Note: If the concentration is < 1 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-atrazine">Note: If the concentration is < 0.001 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-alachlor">Note: If the concentration is < 0.002 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-glyphosate">Note: If the concentration is < 0.7 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-2-4-d">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bis-2-ethylhexyl-phthalate">Note: If the concentration is < 0.006 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trihalomethanes">Note: If the concentration is < 0.08 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-haloacetic-acids">Note: If the concentration is < 0.06 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chlorite">Note: If the concentration is < 0.8 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bromate">Note: If the concentration is < 0.01 mg/L</div>
<div class="product-note in-L6-uranium">Note: Uranium less than < 0.030 mg/L</div>
<div class="product-note in-L6-benzene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-carbon-tetrachloride">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chloroform-trichloromethane">Note: If the concentration is < 0.080 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-ethylbenzene">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-methylene-chloride-dichloromethane-dcm">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-tetrachloroethylene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trichloroethylene">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-xylenes">Note: If the concentration is < 1 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-atrazine">Note: If the concentration is < 0.001 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-alachlor">Note: If the concentration is < 0.002 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-glyphosate">Note: If the concentration is < 0.7 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-2-4-d">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bis-2-ethylhexyl-phthalate">Note: If the concentration is < 0.006 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trihalomethanes">Note: If the concentration is < 0.08 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-haloacetic-acids">Note: If the concentration is < 0.06 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chlorite">Note: If the concentration is < 0.8 mg/L (POU Device System Component)</div>
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<div class="product-note in-L6-bromate">Note: If the concentration is < 0.01 mg/L</div>
<div class="product-note in-L6-uranium">Note: Uranium less than < 0.030 mg/L</div>
<div class="product-note in-L6-benzene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-carbon-tetrachloride">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chloroform-trichloromethane">Note: If the concentration is < 0.080 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-ethylbenzene">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-methylene-chloride-dichloromethane-dcm">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-tetrachloroethylene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trichloroethylene">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-xylenes">Note: If the concentration is < 1 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-atrazine">Note: If the concentration is < 0.001 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-alachlor">Note: If the concentration is < 0.002 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-glyphosate">Note: If the concentration is < 0.7 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-2-4-d">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bis-2-ethylhexyl-phthalate">Note: If the concentration is < 0.006 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trihalomethanes">Note: If the concentration is < 0.08 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-haloacetic-acids">Note: If the concentration is < 0.06 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chlorite">Note: If the concentration is < 0.8 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bromate">Note: If the concentration is < 0.01 mg/L</div>
<div class="product-note in-L6-uranium">Note: Uranium less than < 0.030 mg/L</div>
<div class="product-note in-L6-benzene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-carbon-tetrachloride">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chloroform-trichloromethane">Note: If the concentration is < 0.080 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-ethylbenzene">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-methylene-chloride-dichloromethane-dcm">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-tetrachloroethylene">Note: If the concentration is < 0.005 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trichloroethylene">Note: If the concentration is < 0.004 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-xylenes">Note: If the concentration is < 1 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-atrazine">Note: If the concentration is < 0.001 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-alachlor">Note: If the concentration is < 0.002 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-glyphosate">Note: If the concentration is < 0.7 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-2-4-d">Note: If the concentration is < 0.03 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-bis-2-ethylhexyl-phthalate">Note: If the concentration is < 0.006 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-trihalomethanes">Note: If the concentration is < 0.08 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-haloacetic-acids">Note: If the concentration is < 0.06 mg/L (POU Device System Component)</div>
<div class="product-note in-L6-chlorite">Note: If the concentration is < 0.8 mg/L (POU Device System Component)</div>
