Question: Does a Reverse Osmosis system remove biological contaminants?

Answer: RO systems are capable of removing certain biological contaminants such as Cryptosporidium and Giardia.  The pore size of the RO membrane along with the amount of pressure applied to the water will generally determine the rate of reduction of such contaminants.  The Water Quality Association (WQA) states,  that while RO membranes are reliable for treatment of a range of health contaminants, for foolproof protection against biological contaminants for consumer drinking water systems, WQA suggests that absolute disinfectant (a reduction of contaminants greater than 99.9 percent) be ensured with a post-disinfection system such as ultraviolet light.