Int. J. Environ. Res. Public Health 2012, 9 2762 (2) Use of AISI INOX 316L steel distribution ring with regular microbiological controls, chemical disinfection and SRO system in polyamide; (3) Use of AISI INOX 316L steel distribution ring with regular microbiological controls and daily overnight pulsed thermal disinfection by means of TRO. Table 2. AISI INOX 316L piping. Occasional chemical Regular monthly Regular daily Three dialysis units disinfection (average chemical thermal every quarter) disinfection disinfection Reverse osmosis SRO SRO TRO 27 a,b Technical dialysis posts 21 27 Observation time, months 60 87 36 Sampling, total numbers 180 261 108 CFU, mL/min, average, bacteria 160.4 ± 321.1 1 43.1 ± 76.1 2 15.0 ± 24.6 3 CFU, mL/min, average, mycetes 35.8 ±53.9 4 8.1 ± 8.7 5 1.75 ± 0.41 6 CFU, mL, median bacteria 19.3 21.2 0 CFU, mL, minimum and maximum values bacteria 0–520 0–107 0–2 a Six piping rings of PVC (Table 1); b increase of technical dialysis posts due to enlargement of two dialysis centers; Significance: 1 vs. 2 and 3 vs. 1, 2: p < 0.03; 4 vs. 5, 6: p < 0.02. 2.3. Use of PEX (Polyethylene Thermoplastic Polymer) Piping: Two Centres—See Table 3 PEX piping was used in three successive periods: (1) Use of PEX distribution ring with irregular microbiological controls, occasional chemical disinfection and SRO system in polyamide; (2) Use of PEX distribution ring with regular microbiological controls, chemical disinfection and SRO system in polyamide; (3) Use of PEX distribution ring with regular microbiological controls and daily overnight pulsed thermal disinfection by means of TRO. Table 3. PEX piping. Occasional chemical Regular monthly Regular daily Two dialysis units disinfection (average chemical thermal every quarter) disinfection disinfection Reverse osmosis mono-osmosis mono-osmosis bi-osmosis 23 d 23 d 31 e Technical dialysis posts Observation time, months 24 24 36 Sampling, total numbers 48 48 72 398.1 ± 627 1 33.7 ± 29.9 2 2.4 ± 2.3 3 FU, mL/min, average, bacteria 18.4 ± 38.8 4 0.37 ± 0.84 5 0.30 ± 0.4 6 CFU, mL/min, average, mycetes CFU, mL, median bacteria 101 19.1 0.5 CFU, mL, minimum and maximum values bacteria 0–1,028 0–75 0–0.9 d 23 piping rings of PVC (Table 1); e increase of technical dialysis posts due to enlargement of two dialysis centers; Significance 1 vs. 2, 3 and 3 vs. 1, p < 0.01; Significance 4 vs. 5, 6: p < 0.01.