What is reverse osmosis?

Reverse osmosis, sometimes shortened to the acronym RO, is a filtration process that produces very pure drinking water. A reverse osmosis system forces water, under pressure, through a semipermeable membrane and a number of other filtration steps. A typical RO system has a pre-filter designed to capture larger particles, chlorine, and other substances; a semipermeable membrane that captures more contaminants; an activated carbon filter that removes residual taste, odor, and some organic contaminants; and a storage tank to hold the treated water for use. A storage tank of some size is always required because the RO process is very slow (usually less than 0.1 gpm) and without the system becoming overly large it cannot produce enough water on demand to satisfy normally household uses.