What Is Reverse Osmosis Water?

EPA WaterSense says a reverse osmosis (RO) system 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, and that these systems can potentially remove water contaminants such as lead, volatile organic compounds, PFAS, arsenic, bacteria and viruses. The CDC says reverse osmosis systems remove some types of chemicals from water, including lead, copper, chromium, chloride and sodium, and may also reduce levels of arsenic, fluoride, radium, sulfate, calcium, magnesium, potassium, nitrate and phosphorus.

EPA WaterSense says a typical point-of-use RO system generates five gallons or more of reject water for every gallon of treated water produced, and that some inefficient units generate up to 10 gallons. The CDC says one way to figure out what a water filter removes is to look for an NSF certification on the filter label, and lists NSF Standard 58 as the standard for reverse osmosis systems.

RO water has fewer minerals. A chapter in the WHO report Nutrients in Drinking Water defines demineralised water as water almost or completely free of dissolved minerals as a result of processes including reverse osmosis, and says people who traditionally consume unreconstituted desalinated or distilled water may be consistently receiving smaller amounts of some nutrients than people who drink water from more traditional sources, and are thus disadvantaged if their diets do not provide sufficient intake.