What can cause blue water in a pipe system, and is this safe to use, or drink?
The blue color can come from copper piping.
What Tamie said ^. Typically water that has a blue tinge is caused by copper leaching in the pipes.
Copper pies, leaching is usually caused by low pH,
You should check all of the toilets in the building to see if any of them have the dissolving blue cakes in them, if you find any you may want to check for cross contamination/backflow from the toilet into the potable side. I would not drink the water until you learn exactly what is causing the blue color.