“prism-based attenuators above 100 GHz. I was once designing a secure gigabit data link using the “water hole” at 145 GHz.”
http://www.moviesoundclips.net/download.php?id=2852&ft=wav
... refers to an especially quiet band of the electromagnetic spectrum between 1,420 and 1,666 megahertz...Within this frequency range, interference (attenuation) due to interstellar water molecules is at a minimum, making it a good place (supposedly) to look for signals from other civilizations.
The irony is that "water holes" are places where different species of animals meet and gather in the (terrestrial) wild.