No, it is not due to construction. It has been there for at least 5 years (since I started going to Columbia). It may have originally been caused by construction efforts, but right now the problem is that it's basically impossible to eliminate from the system once it's in there. They tried by raising the temp of the hot water (hence all the warning signs in the bathroom about the scalding water), but the problem is that for people with compromised immune systems or lung disease this still isn't a guarantee.
Actually, NYC tap water is rated some of the cleanest in the nation, if you can believe it.
I'm sure columbia is a little embarrassed about the problem, but as recent studies show most showers have some bacteria in the pipes and/or shower heads. I'm guessing it's not all that uncommon in big buildings like hospitals for some of the dangerous bacteria around there to get in the pipes and of course it's going to live there (damp, wet, dark -- perfect!). Columbia acknowledges the problem and takes steps to make sure everyone's safe, which I appreciate. But yeah, sucks not to be able to shower. And DON'T let them tell you that it's a recent or temporary problem. All future hospital stays at that place are going to be showerless for us, unfortunately.