I would say that depends on the person, I know people who have lived in the NW for years and never contract giardia because they have developed a stronger tolerance after many years of drinking stream water. That being said, here is some info that may help, found this a while back and dug it out of my delicious bookmark collection. Follow the link for more information, testimonials, etc. http://www.miox.com/miox-solutions/The-MIOX-Advantage-safety.aspx Here is some text i pulled from the site. "In contrast to alternative disinfection methods, the safe on-site generation of hypochlorite uses only salt, water, and power as feedstocks. Neither the salt nor the hypochlorite produced is classified as hazardous by the regulatory agencies. The concentration of the generated chlorine solution is below the Hazardous Communications Standard (HCS) safety threshold limit of 1 percent. Although hydrogen gas is evolved from the electrolytic process of on-site generation, automatic venting designs or air dilution systems safely vent this gas to the atmosphere. On-site generation has an excellent safety record, with more than 4,000 units, from a variety of manufacturers, installed worldwide. "