Reverse osmosis is used for a wide variety of water purification purposes, the most common application for RO being drinking water. In fact, RO is the fastest-growing form of in-home water treatment in the U.S.
  A recent study revealed that 70 percent of the people in the Los Angeles area drink only filtered or bottled water. That's a lot of money spent for clean water.
With this growing demand for higher quality drinking water, it's no surprise  homeowners and businesses are buying and installing the same state-of-the-art technology used to process Coca Cola's Dasani and Pepsi's Aquafina bottled water brands. The filtering process used by these bottling giants is nothing more than simple RO filtration. 
The key function of RO, or hyperfiltration, takes place within a tight, semi-permeable membrane that allows only pure water to pass through it. Contaminants such as arsenic, copper, iron, lead, chromium, fluoride, radium, cyanide, nitrates, bacteria, the gas additive MTBE, and pesticides, PCB and benzene can't pass through the membrane because their molecules are, in simple terms, bigger than water molecules, so they can't pass through the holes in the semi-permeable membrane. As a result, RO vastly improves water purity, color and taste.
Unlike charcoal or carbon filters that can become less efficient with each glass of water drawn through them, and which remove only some contaminants, odors, and tastes, an RO system's membrane is self-cleaning. 
As the source water flows through the RO module, it's divided into two streams. One stream is the high quality drinking water that has passed through the membrane. The second stream is the rinsed water that carries the rejected contaminants down the drain. 
There are very few water sources in the United States that challenge the capabilities of an RO system. To operate at a peak performance, the incoming tap water supply should meet the following criteria:

--Water temp: 40 deg. F to 100 F max 
--Pressure: 40-85 psi
--TDS: 1,800 ppm max 
--Turbidity: less than 5 NTU (Nephelometric Turbidity Units) 
--Iron tolerance: 0.2 ppm max 
--Hydrogen sulfide: must be removed 
--Silica tolerance: less than 100 ppm 
--Hardness: more than 10 or 15 gpg should be softened 
--pH range: 3-11

The key components of an RO system include a sediment filter that vastly reduces suspended dust, dirt, sand, rust particles and other sediments, a carbon filter, which reduces chlorine, volatile organic chemicals such as chlorine and pesticides. It's the main cleanser of water odor and taste. And there's also the reverse osmosis filter-the heart of the system. It's responsible for rejecting up to 98 percent of the total dissolved solids in the water. It's here that water purification takes place. 
Another facet to the water quality equation today is water conservation. Even the best residential RO systems use four to five gallons of water for every one gallon produced. Many systems waste as much as 20 gallons just to produce one gallon of product water. 
Zero Waste RO systems by Watts Pure Water eliminate this problem by returning the concentrate water from the RO system back to the home's plumbing (usually the hot water line), resulting in 100 percent efficiency. 
A Zero Waste system takes the water outlet of the sediment and carbon filters and routes it through a solenoid valve and pump before going to the membrane inlet. This provides filtered water to the solenoid and pump which will keep foreign material from damaging them. In some systems the filter configuration allows for water to be routed through the solenoid valve and pump from the water outlet of the sediment filter and then to the water inlet of the carbon filter(s). 
A pressure switch is used to stop the system by opening the circuit to the solenoid valve and pump. When the RO storage tank is full, a pressure switch stops the system from producing more water.
The concentrate water is routed through a flow restrictor as before, except the flow restrictor size is larger to allow for the back pressure of the hot water line. The larger flow restrictor allows the pump to circulate water at approximately a 4-to-1 ratio of concentrate to permeate. The actual flow ratio is the same as with a standard RO system.
The International Association of Plumbing and Mechanical Officials requires the water from the outlet of the flow restrictor to be routed through two check valves before flowing to the hot water supply line. These check valves ensure the hot water will never reach the RO membrane if there is a surge or back pressure in the hot water system. 
In an area where there can be severe restrictions for water use, and very high cost for water, zero-waste technology offers advantages. As consumer awareness sharpens to the realities of higher water costs, and shortages, this smart technology merits a close look.