Answer:
The type of analogy used in the sentence"Water is to moisten as spade is to dig" is function analogy
Step-by-step explanation:
A function analogy also called purpose analogy compares the function of two things, in the sentence "Water is to moisten as spade is to dig" we are comparing one of the basic functions of water which is to get things to moisten with the way we can use a spade which is digging, basically we are referring to their elementary use.