Is the importance of Adachi being Namekian ever explained?

Question

Early on in the series, the story establishes Adachi's drink of choice as mineral water. This prompts Hino to call her a Namekian (since Namekians can survive off of only water).

Adachi drinking mineral water struck me as being important, due to the weight the story seems to give to it; however, it didn't seem to go anywhere. Does it become important later or is there some kind of explanation for what it means?

Answer 1

While it has yet to become any kind of Chekov's gun at the point I've read to (volume 10), it does get explained much later, and elaborates on and connects to some points about Adachi's personality.

Before getting to that, there is an early partial explanation from Adachi that I may have initially glossed over. It is in the first volume on page 133:

When we sat down, the first thing I did was take a sip of my water. It was room temperature and tasted faintly of metal. Same with the tap water back home. That was why I generally preferred mineral water.

The importance of the mineral water and what it says about Adachi comes much later, with the volume 10 chapter The Moon Cradle giving a good picture. Spoilers ahead, particularly on the last quote. However, it is necessary for fully understanding the answer to the question.

It would seem the main point is to establish that Adachi does not care much about food or eating. This complements her previous state, reminding us of how before she met Shimamura, her life was empty and she was apathetic to everything. There are relevant quotes on pages 135, 146, and 156.

Page 135:

"You really don't care about food, huh?"
"That's not true... Well, maybe kinda..." Only when I have to eat something I don't like. Wait, what food don't I like? I don't remember.
"Eh, that's okay. Some people only care about food, so I'm sure it balances out." [...]
Were the two of us balanced, her with a normal interest in food and me with none at all? [..]
"So you have no interest in food. I get it now," she murmured.

Pages 146-147:

"So, what do you want to get?"
"Huh? Oh, uh... bread?"
"Right, gotta have bread. Anything else?"
"Uh, water...?"
"I knew you'd say that!" she exclaimed. [...] "You're like a plant that eats bread," she giggled.
"What?" Apparently, I talked about water too much.

Page 157:

"You can be so incredibly passionate, and yet you sound so bored describing food."
[...]
"[That's because] I... I'm only interested in you, Shimamura."

As I suspected, we get an explanation earlier in volume 8 in the chapter titled Our First Trip, Part 1, and when pressed, Adachi does claim water to be her favorite food. As it is from Shimamura's perspective, as one would expect, the explanation is less complete than the one in volume 10, but one need only read between the lines a bit to reach the same conclusions.

Page 109:

Likewise, Adachi ate her noodles in silence. Was she physically capable of enjoying food at all?

Page 122:

Once again, she showed literally no interest in her meal. Had she ever openly enjoyed eating something? I thought back over my memories of her, but nothing stood out to me. The only thing she seems to take interest in... is me, I realized bashfully.

Page 123:

"Do you have any favorite foods? Sorry if I asked this before, but I really don't remember!" I asked in a light tone of voice.

[...]

She started to say, "Not really," then fixed me with a suspicious look, silently asking me to explain myself.

[...]

Her expression softened, and she began to mull it over. "Favorite foods... Water, I guess?"

"What are you, a plant?"

In addition to claiming water as her favorite food, Adachi also asks Shimamura what her favorite foods are. And upon learning what they are, she silently surrenders them from her own plate and gives them to Shimamura. This is further evidence pointing to our earlier conclusion about what Adachi liking water means. Basically,

that she has no interest in food, and her only interest is in Shimamura.