The Hygienic Standards for Drinking Water (GB 5749-2006) cover 106 water quality indicators, including 20 sensory and general physicochemical indicators, 21 inorganic toxicity indicators, 53 organic toxicity indicators, 4 disinfectant indicators, 6 microbial indicators, and 2 radioactive indicators. 28 water quality reference indicators and limit values are listed in the informative appendix, including 2 microbiological indicators, 2 inorganic indicators, and 24 organic indicators. When drinking water contains these indicators, the limit values can be used for evaluation. And the water quality indicators were separated into conventional and unconventional indicators, improving the operability of water quality monitoring work. It is not very realistic to conduct full testing, and there are some parameters that require the use of professional water quality testing instruments. Therefore, we only need to select a portion of these common drinking water parameters: residual chlorine, total dissolved solids, pesticide residues, and pH concentration.
(1) Residual chlorine (according to the Hygienic Standard for Drinking Water GB5749-2006, the residual chlorine limit is: the contact time with water is ≥ 30 minutes, the limit in the factory water is 4mg/L; the residual in the factory water is ≥ 0.3mg/L; the residual in the water at the end of the pipeline network is ≥ 0.05mg/L;).
(2) Sensory indicators of water, such as chromaticity, turbidity, visible substances to the naked eye, smell, and taste (turbidity limit of 1 NTU in the Hygienic Standard for Drinking Water GB5749-2006).
(3) Total dissolved solids, abbreviated as T.D.S
The conductivity of water, which is the reciprocal of its electrical resistance, is usually used to indicate the purity of water. The national standard GB5749-2006 "Hygienic Standards for Drinking Water" has a limited requirement for the total dissolved solids (TDS) of drinking tap water: TDS ≤ 1000 mg/L, which is obviously far from the international standard. With the development of industry, the variety and quantity of pollutants in water have increased, and this value may no longer meet human drinking standards. When the TDS value exceeds 200, it is considered an industrial water standard, and water above 300 is contaminated by industry. What are the TDS values for various types of water? The TDS value of tap water varies in different regions, with higher values in the northern regions. The TDS value of water in general water plants is around 180-260. If it is deep well groundwater, it should be higher, around 300. In some places, it is possible that the groundwater in industrial areas may be even higher after being polluted. The normal water treated by reverse osmosis (RO) technology is within 50, which is suitable for human consumption.
(4) pH value: According to the "Hygienic Standards for Drinking Water", the pH value of tap water is between 6.5 and 8.5. Water with strong acidity or alkalinity is not good for the human body, so pH value detection is also important.
