The key aspect of the standard is the screening of water quality indices and the setting of their standard limits. The basic process mainly includes the following steps. First, a list of potential contaminants is developed based on the latest drinking water standards at home and abroad, the latest research results and survey data in the field of drinking water and health, and tracking evaluation information on the China SDWQ (2006 edition). Second, a water quality index is identified from the list if its exposure level in drinking water causes health risks or affects sensory acceptability. Monitoring, testing, investigation, and other technical methods are used to determine the presence and exposure level of the candidate indicators in drinking water. Third, the benchmark value of the water quality index is established based on the results of the health risk assessment for the contaminant. Finally, based on the baseline value of the water quality index, a comprehensive assessment is conducted to determine the standard limit value of the water quality index in SDWQ, taking into account the contaminants detection technology, the treatment process, risk management measures, and other factors. The technical route of standard limits setting is illustrated in Figure 1.
In accordance with the above principles, the 2022 edition of the China SDWQ reduced the number of mandatory indices from 106 to 97 (3). Four indices were added, including perchlorate, acetochlor, geosmin, and 2-methylisoborneol. A total of 13 indices were removed, including heat-resistant coliforms, trichloroacetaldehyde, hydrogen sulfide, cyanogen chloride (measured as CN-), hexachlorocyclohexane (total), parathion, methyl parathion, lindane, dichlorodiphenyltrichloroethane, formaldehyde, 1,1,1-trichloroethane, 1,2-dichlorobenzene, and ethylbenzene. The standard limits for 8 indices were adjusted, including nitrate (N), turbidity, permanganate index (measured as O2), free chlorine, boron, vinyl chloride, trichloroethylene, and dimethoate. The number of non-mandatory indices increased from 28 to 55, including pollutants such as nitrosodimethylamine, perfluoro caprylic acid, perfluorooctane sulfonate, and iodide. The 2022 edition of the China SDWQ has unified the assessment requirements of urban and rural water supply quality, strengthened the scientific and safety of disinfection, and improved the management requirements of sensory properties of drinking water, which is more in line with the current requirements of drinking water quality in China.