Reverse Osmosis filtration cleans water by taking out the totally dissolved solids (TDS) which contaminate the water. Although city water treatment removes the dirt and debris and adds chlorine to prevent the spread of diseases, it does not remove the dissolved solids from the water. Also with the increasing pollution of our surface and ground water, it is more important than ever to have a way to remove these contaminants at the point of use in your home.

Reverse Osmosis membranes used in water filtration systems can on average, remove 95% of dissolved contaminants from water (see table at left). Only 1% of the city water entering the home is used for drinking and cooking — about 2-3 gallons per day— where the average home uses 300 gallons per day or more. So it makes sense to clean just the water needed for drinking and cooking at home. City water is available at the home from already-installed water mains and has the required pressure of 60 to 75 psi to make the reverse osmosis system work.

Osmosis is a naturally occurring process in human and animal membranes. Salts in the body fluids build up osmotic pressure, forcing water molecules through the living membranes in our bodies. In under-sink reverse osmosis systems, pressure from the city water overcomes the “salt” pressure of the dissolved materials and forces the water molecules through a synthetic thin film membrane, leaving the dissolved salts behind. The city water enters the membrane filter element, and two streams leave; the clean water and the water containing the dissolved solid residue, called brine, which is discarded to the drain. On the comparative chart below, reverse osmosis removes the smallest of material molecules, from 1-micron down to 1- Angstrom. For particles larger than 1-micron, particle filters are used ahead of the RO membrane to prevent plugging of the tiny membrane pores in the reverse osmosis membrane.

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