This is the first indicator that Kubrick uses outside sound (not necessarily soundtrack sounds) in bridging scenes or sequences together.
During No.6, the scene opens with Danny playing with water as he talks to Tony about why he doesn’t want to go to the hotel.
The scene transitions and Wendy is also “playing with water”: she’s doing the dishes.
This both conveys to the viewer of the mechanism but also shows you that Danny is aware of (and can mimic) what his parents are doing.
In this image · No.6
Sound Reflection as Structure
Having the sound link from Danny in the bathroom to Wendy at the sink creates the semiotic connection in sound. Kubrick has Danny in the bathroom in Image 129, with his hands unseen. Water is heard running and splashing. When we go to Image 130, Wendy is doing the dishes and running water is shown and heard.
Kubrick makes this choice to show other reflections of Danny’s awareness of his parents’ actions across the film, sometimes spatially and therefore thematically, and sometimes literally within the same space but shown symbolically. See: Proximity; Danny’s Awareness of Problems Caused by Parents.