1.1 This specification covers requirements for water suitable for use in methods of chemical analysis and physical testing. Four grades are specified: Type I Type II Type III Type IV Electrical conductivity, max, µS/cm at 298 K (25°C) 0.056 1.0 0.25 5.0 Electrical resistivity, min, Mcm at 298 K (25°C) 18 1.0 4.0 0.2 pH at 298 K (25°C) A A A 5.0 to 8.0 Total organic carbon (TOC), max, µg/L 50 50 200 no limit Sodium, max, µg/L 1 5 10 50 Chlorides, max, µg/L 1 5 10 50 Total silica, max, µg/L 3 3 500 no limit Microbiological contamination-When bacterial levels need to be controlled, reagent grade types should be further classified as follows: Type A Type B Type C Maximum heterotrophic bacteria count 10/1000 mL 10/100 mL 100/10 mL Endotoxin, EU/mlB 0.03 0.25 not applicable AThe measurement of pH in Type I, II, and III reagent waters has been eliminated from this specification because these grades of water do not contain constituents in sufficient quantity to significantly alter the pH. B EU = Endotoxin Units. 1.2 The method of preparation of the various grades of reagent water determines the limits of impurities and shall be as follows: 1.2.1 Type I grade of reagent water shall be prepared by distillation or other equal process, followed by polishing with a mixed bed of ion exchange materials and a 0.2-µm membrane filter. Feedwater to the final polishing step must have a maximum conductivity of 20 µS/cm at 298K (25°C). 1.2.2 Type II grade of reagent water shall be prepared by distillation using a still designed to produce a distillate having a conductivity of less than 1.0 µS/cm at 298 K (25°C). Ion exchange, distillation, or reverse osmosis and organic adsorption may be required prior to distillation if the purity cannot be attained by single distillation. Note 1 - Because distillation is a process commonly relied upon to produce high purity water, the levels specified for Type II reagent water were selected to represent the minimum quality of water that a distillation process should produce. 1.2.3 Type III grade of reagent water shall be prepared by distillation, ion exchange, continuous electrodeionization reverse osmosis, or a combination thereof, followed by polishing with a 0.45-µm membrane filter. 1.2.4 Type IV grade of reagent water may be prepared by distillation, ion exchange, continuous electrodeionization reverse osmosis, electrodialysis, or a combination thereof. 1.3 The choice of one of the various grades may be designated by the method or by the investigator. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.