To discuss the composition of “water family” in the five elements theory, and to explore the similarities and differences between these family members. Methods: Using Wittgensteins family-resemblance theory, analyze members of the “water family”: water, north, black, salty, winter and kidney. Results: The members of “water family” have family resemblance, and they are associated by analogy. Conclusion:The members of “water family” have interconnected resemblance, and they are associated by analogy. The features of the “water family” are the summed-up features of each family member, in return they are given back to each family member. The traditional Chinese medical theory was based on the five elements theory. Therefore, the human organs had been classified according to the five elements theory. So it will be easily understood that some functions of kidney are endowed with the features of the “water family” rather than naturally possessed.