So you noticed the water was purple and wanted an answer huh?
It's purple because it's 70% Fluoride. Legend has it that Grover Breign Jr. ordered fluoridated water as soon as the fad caught on with the mainland. Adding 0.7ppm to the water, he was successful in preventing tooth decay among the employees.
Dr. Breign knew little of the program until he got a toothache in 1940. Dr. Moco explained that it was just a matter of poor hygiene and dental exposure due to the lack of a lower jaw or lips, but Breign, as soon as he heard about how fluoride was meant to prevent tooth decay, blamed the low dosage in the water and ordered it doubled. When he got another toothache a month later, he ordered the rate googleplexuppled. As this would have resulted in several thousand tons of Fluoride per gram of water, Breign relented and settled for a 700,000ppm dosage.
No instances of tooth decay have been reported since, though fluoride poisoning and cancer are up 30,000%, and numerous employees began feeling favorable toward communism.