Michael,
The large building is, indeed, the water works. I am not sure when it it was shut down, but I believe may have been about the time when the "new" water tower (current one), was built on south Main Street, just north of 55th street. At that time, a more modern electric pumping station was built adjacent to the tower. The original tower, which appears in at least one of the DG photos, was a true cylindrical brick tower, as opposed to the present steel tank design.
In my childhood era of the 1940s -1960s, the water works building was significantly modified and became Albert Zollengers manufacturing company. They made some sort of plastic components. Today, the building still exists, but has been further modified, I believe, as an office building. I don't know what company currently occupies it. I think if you go around to the track side of the building, you can still see evidence of it's original construction. As Zollengers, it retained a lot of the water works character. Today, that is difficult to visualize. The building was about five blocks from my parent's home on Seeley Ave.
By the way, in case some didn't figure it out. there are "previous-next" tabs at the top of the photo accessing many more photos or the RR and DG. I don't know if it is the DGHS's entire collection or not, but I plan to check their site to see if any more photos are available. The photos have a download tab near the bottom so they can be saved to your computer, albeit with the DGHS log ghost imbedded. Thanks for posting the link. That blew an hour, this morning!
Bill Barber
Gravois Mills, MO