Quality control for a 14- to 18-megohm-cm deionized water supply

We studied the quality control for a 14- to 18-megohm-cm deionized water system with multiple outlets. The quality of water was determined by measuring specific resistance, performing a total colony count, trace metal analysis, and high-performance liquid chromatographic analysis. The specific resistivity of water was at the level of 17 to 18 megohms-cm at the recirculation loop and greater than 10 megohms-cm at the individual faucets. The microbial content was consistently less than 100 colony-forming units/mL. Periodic trace-metal analysis indicated less than 1 microgram/L of copper, bismuth, zinc, cadmium, mercury, thallium, and lead. High-performance liquid chromatographic analysis, as determined by the absorbance of the highest peak by ultraviolet and fluorescence spectroscopy, indicated less than or equal to 0.001 absorbance unit. Our experience suggests that maintaining laboratory water at 14 to 18 megohms using a plastic system with plastic faucets eliminates the likelihood of bacterial organic and trace-metal contamination of the water.