This here a lesson learned from people who work on construction sites: “Water is the enemy”.
At least if you are building a tunnel or dig a hole for a cellar or basement garage. Or for an underground train line.
So to keep water from flooding your plans the workers build nice pipes over and under the street level. Sometimes red, like in Berlin, and sometimes blue. Here we are: Cologne in September 2011.
Some more ideas for appropriate colours to paint those pipes with? We guess they should be blue. Well, there’s water inside…