odor and taste
Clean water bodies are odorless and tasteless, while natural water bodies may have some odor and taste due to dissolved minerals, the reproduction, death, and decay of animals, plants, and microorganisms in the water. Water bodies polluted by domestic sewage and industrial wastewater often have a strange odor. The main measurement methods include qualitative description method and threshold method.
（1） Qualitative description method
1. smellyTake 100mL of water sample and place it in a 250mL conical flask. The inspector relies on their own sense of smell to smell its odor at 20 ℃ and after boiling and slightly cooling. Use appropriate words to describe its odor characteristics and report the odor intensity according to the classification in Table 3-11.

outside3-11 Odor intensity level

2. Only clean water or water samples that have been confirmed to be harmless to the human body through oral contact can undergo taste testing. The method is to take a small amount of water samples at 20 ℃ and boiled and cooled separately, put them in the mouth, taste their taste, describe them with appropriate vocabulary (sour, sweet, salty, bitter, astringent, etc.), and refer to the taste intensity levels given in Table 3-12.
outside3-12The Four Taste Representative Substances

（2） Odor threshold method
This method involves diluting the water sample with odorless water until the lowest identifiable concentration of odor is detected (known as the "odor threshold concentration"), which is used to represent the threshold of odor. The dilution ratio of a water sample to the point where a foul odor is detected is called the "odor threshold", which refers to
Key points of inspection operation: Prepare a water sample dilution series in a conical flask with water sample and odorless water (do not let the inspector know the dilution ratio), and heat it on a water bath to 60 ± 1 ℃; The inspection personnel take out the conical flask, shake it 2-3 times, remove the stopper, smell its odor, compare it with odorless water, determine the dilution sample that just smells the odor, and calculate the odor threshold. If the water sample contains residual chlorine, it should be inspected once before and after dechlorination.
Due to differences in olfactory sensitivity among inspectors, the test results for the same dilution series of water samples may be inconsistent. Therefore, it is generally recommended to select at least 5 olfactory sensitive personnel for simultaneous testing, and take the geometric mean of the test results of each odor inspector as the representative value.
Generally, odorless water is produced by using tap water and granular activated carbon. The residual chlorine in tap water can be removed by titration with sodium thiosulfate solution. Distilled water can also be used to produce odorless water, but commercially available distilled water and deionized water cannot be directly used as odorless water.