Detection of environmental conditions at the place of origin

1. Total bacterial count 1.1 Plate counting method 1.1.1 Scope This standard specifies the use of plate counting method to determine the total bacterial count in drinking water and its source water. This method is applicable to the determination of total bacterial count in drinking water and its source water. 1.1.2 Terms and Definitions The following terms and definitions apply to this standard. 1.1.2.1 Standard plate count bacteria The total number of colonies in 1 mL of water sample obtained after cultivation on nutrient agar under aerobic conditions at 37 ℃ for 48 hours. 1.1.3 Culture medium and reagents 1.1.3.1 Nutrient agar 1.1.3.1.1 Composition: A protein knee 10 g B beef extract 3 gc sodium chloride 5 g D agar 10 g~20 g E distilled water 1 o00 mL1.1.3.1.2 Preparation method: Mix the above ingredients, heat them to dissolve, adjust the pH to 7.4~7.6, divide them into glass containers (if using agar with high impurities, filter first), sterilize them at 103.43 kPa (121 ℃, 15 lb) for 20 minutes, and store them in a cold and dark place for future use. 1.1.4 Instrument 1.1.4.1 High pressure steam sterilizer. 1.1.4.2 Dry heat sterilization box. 1.1.4.3 Incubator 36 ℃ ± 1 ℃. 1.1.4.4 Electric furnace. 1.1.4.5- Balance. 1.1.4.6 Refrigerator. 1.1.4.7 Magnifier or colony counter. 1.1.4.8 pH meter or precision pH test paper. 1.1.4.9 Sterilization test tubes, Pingmeng (diameter 9 cm), graduated straws, sampling bottles, etc. 1.1.5 Inspection steps 1.1.5.1 Drinking water 1.1.5.1.1 Using sterile operation method, take 1 mL of fully mixed water sample with a sterile straw, pour it into a sterile plate, pour about 15 mL of melted and cooled nutrient agar culture medium to around 45 ℃, and immediately shake the plate to fully mix the water sample with the culture medium. During each test, parallel inoculation should be performed, and a separate plate should be used to pour only nutrient agar culture medium as a blank control. 1.1.5.1.2 After cooling and solidification, flip the plate so that the bottom is facing upwards. Incubate in a 36 ℃± 1 ℃ incubator for 48 hours and perform colony counting

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