Water treatment in swimming pools and spas is designed to protect the health and comfort of swimmers and bathers. The primary objective is to prevent the growth of germs and bacteria by maintaining a safe level of sanitizer (chlorine or bromine and/or ozone). Most dangerous are E. coli in pools and A. Pseudomonas in spas. They both can cause fatal diseases.
Numerous studies by health departments in many countries have shown that the Oxidation-Reduction Potential (ORP or Redox) generated by the sanitizer is the most reliable indicator of both sanitizer activity and sterilization of germs and bacteria.