Microbiological quality assurance of purified water by ozonization of storage and distribution system.

Purified water storage and distribution systems at ambient temperature are highly susceptible to microbial contamination and formation of biofilm. The impact of two disinfection regimens with ozone as a function of time, the heterotrophic plate counts (HPC), and the concentration of total organic compounds (TOC) in purified water were investigated over a period of 4 years. We have established that concentrations of ozone of 70 +/- 20 ppb in the production regimen and 250 +/- 50 ppb in the disinfection regimen are sufficient to maintain a low bioburden and low TOC in a recirculating distribution system. The purified water that entered into the distribution system has low HPC (0.01 CFU/mL), indicating a reduction by ozone in the storage tank by up to approximately 120-fold. Over 4 years, 94-98% of the microbial counts were in the category 0-5 CFU/mL, and none in category > or =50 CFU/mL. In spite of increased TOC in the inlet water, up to 40 ppb, the microbial counts in purified water in the distribution loop were unaffected. The study emphasizes that the critical points regarding microbial contamination of the purified water system are user point valves and the tubes used for transferring water to equipment. The specified ozone level prevents microbial growth and formation of biofilm in the distribution system that might otherwise endanger the water quality by sporadic release of microbes.