Reverse osmosis (RO) is generally recognized as the best system for purifying water while retaining good taste. The EPA recommends reverse osmosis filters for microbiologically safe water. Yet, an RO system alone will still allow certain waterborne germs to pass through. To knock out these types of contaminates, most RO systems incorporate some additional type of filtering, usually a replaceable carbon post filter.
What Is Reverse Osmosis?
Reverse osmosis involves the passage of potable water through a semi-permeable membrane. In a normal osmotic reaction, water containing a dissolved substance in low concentration will flow through a membrane to the side containing a higher concentration of the dissolved substance. If pressure is applied to the side having the higher concentration of solution, the flow of water can be stopped or even reversed. When the flow is reversed, this is called “reverse osmosis.” In this case, it is the water that has less dissolved substance that is desirable; this is the purified water.
How Do Reverse-Osmosis Systems Work?
The reverse-osmosis water filter is usually installed beneath your kitchen counter. The filter commonly consists of five components: one or two sediment pre-filters, the RO membrane filter, a drain for reject water, a small treated water storage tank, and a carbon post-filter. In addition, an air gap is built into the faucet; this serves as a sanitary device by preventing wastewater from flowing back into the filter.
Most reverse-osmosis systems purify water in 3 to 5 phases. The early phases use pre-filters to remove particles of dirt and sediment, chemical contaminants, certain microorganisms, and odors; a middle phase employs the RO membrane itself to eliminate dissolved solids, metals, and other microorganisms; and a final phase actuates a carbon (charcoal) post-filter to eradicate any remaining traces of chemicals and odors, thereby improving the quality and taste of the water.
