Usual is a synonym of Normal. 
you are likely to find Teenager in/at/on Roof. you are likely to find Water in/at/on Roof. you are likely to find Water in/at/on Mud. Mud is related to Liquid. 
Usual <--Synonym--> Normal 
Teenager --AtLocation--> Roof <--AtLocation-- Water --AtLocation--> Mud <--RelatedTo--> Liquid 