They mentioned it (don' remember in which ep). A symbol of the conditions of poor and underdeveloped societies whose drinking water and food are monopolized by developed and rich societies.
The best part was the part that showed all the classes were completely randomly selected by the characters. Like someone who is born in a poor family in Somalia or the child of a rich person in a developed country.
As you may know, the industrial waste of developed countries is sometimes dumped in non-developed countries in the term of "waste trade" or "waste dumping". And it has always been the way in the society that the poorer classes are condemned to endure difficult environmental conditions that may be the result of the rest of the society and their own consumptions.
The one with 880 ep "Chief Inspector (1971)" has totally different style, and happening in their own current years and it's episodic drama. This one, just has gotten some inspiration from that plus ost and music.
I loved anime but this one I think something was missing. There were so many holes. e.g. why Seol Kang Woo's friend scarified his life?! or why he was crying when he found Jung Soo In in the museum at the end? and so many more. Also I think directing was a little bit weak .
As they're showing the neighbour who's not on the screen so much in the main characters section. I can say the person behind the phone and at the end of the corridor also in the car with ML that MF saw his hand with blue bandaid. Neighbour grandpa and she are Ma Gang's boss.
And it has always been the way in the society that the poorer classes are condemned to endure difficult environmental conditions that may be the result of the rest of the society and their own consumptions.