Reverse osmosis pushes water through a thin film composite (TFC) membrane so fine, about 0.0001 micron, that water passes through and most dissolved minerals, metals and chemicals do not. What the membrane holds back is rinsed away to the drain.
The table shows how much of each contaminant a standard TFC reverse osmosis membrane typically rejects. These are estimates based on industry standards and Crystal Quest internal testing. They are typical values, not a guarantee: your results depend on your water.
What people ask about most
Every contaminant, by group
Dissolved solids and hardness
| Total dissolved solids (TDS) | 95 to 99% |
| Hardness | 93 to 97% |
Heavy metals
| Aluminum | 97 to 98% |
| Cadmium | 96 to 98% |
| Chromium | 96 to 98% |
| Copper | 97 to 99% |
| Iron | 98 to 99% |
| Lead | 96 to 98% |
| Manganese | 96 to 98% |
| Mercury | 96 to 98% |
| Nickel | 97 to 99% |
| Silver | 95 to 97% |
| Zinc | 98 to 99% |
Arsenic, fluoride, nitrate and other compounds
| Ammonium | 85 to 95% |
| Arsenic | 94 to 96% |
| Chromate | 90 to 98% |
| Cyanide | 90 to 95% |
| Ferrocyanide | 98 to 99% |
| Fluoride | 94 to 96% |
| Nitrate | 93 to 96% |
| Selenium | 97% |
Minerals and salts
| Bicarbonate | 95 to 96% |
| Boron | 50 to 70% |
| Bromide | 93 to 96% |
| Calcium | 96 to 98% |
| Chloride | 94 to 95% |
| Magnesium | 96 to 98% |
| Phosphate | Over 99% |
| Polyphosphate | 98 to 99% |
| Potassium | 92% |
| Silica | 85 to 90% |
| Silicate | 95 to 97% |
| Sodium | 92 to 98% |
| Sulfate | Over 99% |
| Sulfite | 96 to 98% |
Radioactive elements
| Radium | 97% |
| Radioactivity | 95 to 98% |
Pesticides and other chemicals
| Detergents | 97% |
| Herbicides | 97% |
| Insecticides | 97% |
Microorganisms
| Bacteria | Over 99% |
| Pyrogens | Over 99% |
| Viruses | Over 99% |
What changes the numbers
- Your water: the mix and amount of minerals and chemicals in it.
- Temperature and pressure: how warm the water is and how hard it pushes on the membrane.
- pH: some contaminants, such as boron and silica, are rejected better at some pH levels than others.
- Membrane care: a membrane works best when its pre-filters are changed on time and chlorine never reaches it.
About bacteria and viruses: a reverse osmosis membrane rejects them too, but reverse osmosis is not a disinfection method. Use it on water that is safe to drink, and add UV where water needs disinfecting.
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