Some of these states, California for instance, require that all water treatment devices which are designed to reduce specific contaminants from water supplies be tested in accordance with testing protocols specified in the California Code of Regulations Title 22. California has chosen National Sanitation Foundation (NSF) Standard 53 Protocols for drinking water treatment units for health effects, NSF Standard 58 for reverse osmosis drinking water treatment systems, NSF Standard 44 for cation exchange water softeners, and NSF Standard 62 for drinking water distillation systems. In California the systems and manufactures meeting the testing requirements accepted by the Department of Health Services receive certification for making health related contaminant reduction claims. Without this documentation, California will not allow the sales of any product within the state if claims are being made which don't have the required supporting test data. Here is a list of some of the items which are considered as health related contaminants:

Total coliform bacteria and turbidity, Arsenic, Barium, Cadmium, Chromium, Fluoride, Lead, Mercury, Nitrate, Selenium, Silver, Benzene, Carbon tetrachloride, 1,
2-Dichloroethane, 1,1-Dichloroethylene,
p-Dichlorobenzene, Endrin, Lindane, Methoxychlor, Total Trihalomethanes, Toxaphene, Trichloroethylene, Toxaphene, Trichloroethylene, 1,1,1-Trichloroethane, Vinyl chloride, 2,4,5-TP (Silvex), 2,4,-D, and Radium-226 & 228.

Whenever you see an advertisement or hear someone saying their system will remove any one or more of these health related contaminants, ask to see the Data sheet which attests to this fact.