How Safe Is Reverse Osmosis Purification?

Reverse osmosis (RO) systems create fresh water at desalination plants worldwide. Smaller versions of these systems also are prevalent in households to provide purification of municipal and well water coming into the home. Concerns exist, however, as to whether RO systems can reliably deliver safe drinking water.

History

• Late in the 1940s, a push was on to find a viable way to desalinate brackish water and seawater. Federal and state funding helped researchers at the University of California, Los Angeles develop the first reverse osmosis (RO) membrane. It was made of cellulose acetate and could reject salt while passing fresh water with reasonable pressure and production rates. This invention has led to fresh water delivery to places such as the Middle East and North Africa where natural sources of fresh water are scarce.

Function

• Whether large-scale RO systems or small home units, RO systems work on the same principle. Water is forced under pressure through a membrane filter with microscopic holes. These holes are only big enough to allow water molecules to pass through. Molecules of salt and those of other substances larger than water molecules are screened out of the water by the filter. The purified water that has passed through the filter is collected for human consumption.

Limitations

• The main disadvantage of RO systems is that people use them for water purification instead of salt removal. Home systems especially are marketed as being capable of providing fresh, healthy water for drinking and cooking. This claim, however, is not entirely true. Any substance in the water whose molecules are the same size or smaller than those of water will pass through the membrane filter and end up in the filtered water supply. Some of these substances, including prescription medications, chlorine and many herbicides and pesticides, can be dangerous to human health.

  In addition, RO filters remove trace minerals like magnesium and calcium that can be essential for good health.

Warning

• A report published by the University of North Dakota states that RO filters remove virtually all microorganisms. The same report cautions, however, that RO membranes can easily have pinhole leaks that would allow harmful bacteria into the purified water supply. Therefore, people should not rely on RO systems for the elimination of bacteria. Instead, the source water supply should be free of harmful microorganisms.

Conclusion

• Reverse osmosis filtration is safe as long as users understand the limitations and use RO appropriately. It is a good method of desalination, but other filtration systems may be better depending on the nature of contaminates in the source water to be filtered.