Found on top of Morgan Manufacturing, an event space, office complex and innovation lab, this colorful water tank has been a part of the building since it was built in 1855. This water tank and building was previously home to Salisbury by Honeywell. The water tank used to bear Salisbury Electric 1855 on its side (as seen above). Although it's not exactly clear when the water tank was painted, it has been a beautiful addition to the neighborhood since at least when blogger Daniel Schell's posted about it in 2016.
Sources: https://danieldschell.wordpress.com/2016/01/05/could-this-be-my-new-favorite-chicago-water-tank/ https://www.dnainfo.com/chicago/20140825/west-loop/morgan-mfg-six-building-event-office-compound-open-september https://www.salisburybyhoneywell.com/en/about/history