That website also says that the Chicago Journeymen Plumbers group does the dying, as it has for the last 50+ years. What's funny is that the dye that is used appears orange when first added to the water, and then it miraculously turns "Irish green" within minutes. About 40 pounds of vegetable dye are used, and the process takes about 5 hours.
Other things that "go green" for St. Patrick's Day? The Leaning Tower of Pisa, the fountain at the White House ( a new tradition, started by the Obamas, to remind them of Chicago), the downtown canal in Indianapolis, and all the fountains in Savannah GA.
And don't forget that most Irish pubs - everywhere - will have green beer. No less an authority than Betty Crocker has a recipe for green beer!
According to Betty, the best way to do it is to use a very light colored beer (pale ale, pilsner). Use liquid green food coloring (the kind that comes in little squeeze bottles). Squeeze some (4-6 drops) food coloring in the bottom of your pint glass, and then slowly pour the beer in to the food coloring. This way, you don't have to stir the beer, which could make it go flat. Oh, and one more thing: if you think adding blue food coloring to yellow beer will give you green beer, experts say you're wrong! You'll end up with turquoise, and nobody wants to drink turquoise beer!