Figure 1.

Anyone who has sat through a high school science class may remember the term "osmosis."

Residential Systems

Typical countertop or under-sink residential systems are referred to as "low-pressure"

Commercial/Industrial Systems

High-pressure reverse osmosis systems typically operate at pressures between 100 psig and 1,000 psig, depending on the membrane chosen and the water being treated. These systems are typically used in industrial and commercial applications where large volumes of treated water are required at a high level of purity.

Most commercial and industrial systems use multiple membranes arranged in parallel to provide the required quantity of water. The processed water from the first stage of treatment can then be passed through additional membrane modules to achieve greater levels of treatment of the finished water. The reject water can also be directed into successive membrane modules for greater efficiency, though flushing will still likely be required when concentrations reach a level where fouling is likely to occur.

High-pressure industrial units typically provide from 10 to thousands of gallons of water per day, with an efficiency of 1-9 gallons of reject water per gallon of treated water. Water purity can be as high as 99%. These systems tend to be larger and more complicated than low-pressure systems, and this is reflected in their cost. Commercial and industrial units can range in cost from $1,000 to tens of thousands of dollars for a large, multi-module unit that can provide desalinated drinking water for a resort facility or water bottling plant.

What RO Treats

RO can treat for a wide variety of health and aesthetic contaminants. Effectively designed RO equipment can treat for aesthetic contaminants that cause unpleasant taste, color or odor problems, such as a salty or soda taste caused by chlorides or sulfates.

RO can also be effective for treating health contaminants such as arsenic, asbestos, atrazine (herbicides/pesticides), fluoride, lead, mercury, nitrate and radium. When using appropriate carbon pre-filtering, additional treatment can also be provided for such "volatile"