The water department is located in the southern end of District 7, not too far from A Certain Middle-High School. The facility is comprised of two main buildings, one fenced-in, flat-roofed, concrete building and a smooth, rectangular roofed, high-rise building, containing several septic tanks stacked vertically. A reinforced concrete pathway surrounded by glass connects the two buildings.
The high-rise building contains water purification equipment, with vertically stacked water tanks containing culture mediums for water purification microbes (浄水微生物 Jōsui Biseibutsu?), which consume bacteria. The floors in the high-rise building have with no internal, dividing walls, with the majority of the space taken up by a large square hole opening onto a tank 40m long, 40m wide and 5m deep. Normally filled with water, the tanks also contain mud at the bottom of the tank acts as the culture medium for the water purification microbes. A metal ladder is fitted to the wall of the tank for maintenance work.
- Main article: Element Arc
Early in the morning on December 8th, in the middle of the abnormal heat wave and the Elements' assault on the city, a party comprised of students from A Certain High School made their way to the water department in hopes of obtaining some of the water purification microbes used there, in order to purify the pool at A Certain Middle-High School and solve their water shortage problems. After using a glider and updrafts from the heat to access the roof of the flat building, they made their way to the purification building.
After finding that the cultivation medium was still alive, they managed to acquire some of the cultivation mud remaining in the nearly empty tank. On the way back however, the group came under attack from the Elements, whom they'd forgotten preferred cool, dark places. During the attack, Kamijou Touma was separated from his classmates, who managed to escape across the passageway to the flat building before a high-pressure water jet destroyed it. Shortly afterwards, the Elements in the facility were decimated by Misaka Mikoto using her newly acquired Anti-Art Attachment.
- ↑ Shinyaku Toaru Majutsu no Index Light Novel Volume 16 Chapter 1 Part 1
- ↑ 2.0 2.1 2.2 2.3 Shinyaku Toaru Majutsu no Index Light Novel Volume 16 Chapter 1 Part 4