There are so many potential questions raised with respect to runoff water, so I'll just stick with one:
When I was a kid I was taught to let the water of a drinking fountain run for 10 seconds before drinking. This was to let the water run cold, and, we were always told, to remove toxins.
Would running that extra water be a problem of Bal Tashhith (prohibition against wasting)?
What about just the water that runs off while you're drinking?