I have been in pond construction for over 15 years and have been researching NSPs for the last 8. What I have gleaned from this research which included conversations with the CDC and with the North American representative for the largest NSP contractor in Europe is that there is NO way to guarantee that the water will be as safe as a conventional swimming pool. Plants can and will remove chemical pathogens from the water column but have no prophylactic effect on organic pathogens such as E coli, fecal coliform bacteria or other pathogenic organisms. If one is to eliminate the commonly used sterilizer, Chlorine, then it must be replaced with something else of similar effectiveness such as a commercial grade UV sterilizer or Ozone generator. Periodic testing is also required in order to ascertain that the proper level of disinfection is being applied.
