At first glance, these images may not seem to be permeated with water, but look closely.

Notice the pattern dyed into the hanging cloth screen in the top image--rippling waves in a large body of water.  And notice the pattern on the orange box serving as a makeshift pillow--waves. (Notice also how unrealistic these images often are. She would be lucky not to break her neck in given the position she is in, the height of the box, and the direction of the forces being applied--a point that will come up later.)

In the bottom image, notice the large water cistern (far left), partially opened. And notice the water pouring out of the woman's large basin. She is apparently a servant caught by surprise (a common situation in this genre).

Notice that in the top image, the water-patterned cloth screen is in motion, as are the vigorous waves on the box. Below, woman's cooking or washing water is also in motion, and it is also likely that the kettle in the background contains water (or some kind of liquid), which is being agitated by the flames.

So these images are full of agitated or moving sexual energies and, likewise, full of images of agitated or moving water.

If women had produced erotic images in Tokugawa Japan (and some did, privately, but nearly all extant shunga were produced by men), perhaps they would have been permeated with yang images such as flames, sunlight, or heat.