Not sure why this comment is being downvoted. It's technically accurate. The definition of "reservoir" implies that a body of water is being collected or stored for later use. A reservoir need not be artificially constructed (i.e., a well or drainage pool), but in order to be a "reservoir," it needs to be put to use or accessible for use.
I am not a PR person myself, but I think the vast majority of laypeople who stumble across the headline "large, distant reservoir" would assume that the source is tappable. They might also ignore or not really understand the issue of the 12 billion light years -- or the inconvenience, to say the least, of the quasar nearby.
I actually think this was a good move by the PR. I think most people understand that space travel is in its newest form and by calling it a reservoir NASA is challenging science so that one day this distant water can become a practical reservoir.
