I was about to post an item about Tajikistan and its hydropower potential when I viewed Jared Simpson's 29 August 2008 Waterblogged.info post in which he talks about speedblogging and also gives me a mention or two (and a lot more stature than I deserve).
One of these mentions deals with the question of whether "ground water" should be one word or two. My esteemed opinion: it doesn't matter, as long as you are consistent.
I generally use "ground water" as two words, although when I recently looked at my 1975 PhD dissertation, I was surprised to discover that I had spelled it "groundwater". This I attributed to my dissertation advisor, the late Dr. Eugene S. Simpson. Gene was a master of the English language. In fact, he had originally planned to get a Bachelor's degree in English from City College of New York (now City University of New York), but World War II had turned him towards civil engineering and he got his BSCE.
When I started writing my dissertation, I used "ground water"; Gene changed it to "groundwater". When I tried to make my case, citing that since we spelled the following as two words - surface water, lake water, ocean water, soil water, etc. - we should be logical and spell it as 'ground water', Gene replied, "English is not a logical language." No response to that.
He then explained that much of the early work in ground water hydraulics had been done by German-speaking scientists and engineers: Philipp Forchheimer, Gunther and Adolf Thiem, Karl Terzhagi, et al. As is the custom in German, "Grund" and "Wasser" were combined to form "Grundwasser". Many of the early English-speaking water engineers and scientists adopted this convention. But many didn't, following my logic.
In retrospect I have flip-flopped throughout the years. Whether I used "groundwater" or "ground water" largely depended upon which ground water book I was using for my classes: Groundwater by R. Allan Freeze and John Cherry; Groundwater Hydrology by Herman Bouwer; Applied Hydrogeology by Bill Fetter (who used two words); Hydraulics of Groundwater by Jacob Bear.
I should also note that the National Ground Water Association and its flagship journal Ground Water, use two words, but Editor-in-Chief Mary Anderson prefers one word. I kid NGWA Executive Director Kevin McCray that in the logo, "ground" and "water" seem to be creeping inexorably towards each other. Does "ground water" in that logo look like one word or what?
The USGS also uses two words.
One advantage to using one word: there is no ambiguity about hyphenation when it is used as an adjective. Is it "ground-water hydrology" or "ground water hydrology"? Again, be consistent. But don't ever write "surface and groundwater" when you mean "surface water and groundwater." However, "surface and ground water" is okay, as is "surface water and ground water." Ah, English!
There actually has been a fair amount of discussion on one word vs. two, including a brief article by A. Ivan Johnson (1986), which comes down strongly on the side of two words (the article starts at the bottom of the first page):
Then Allan Freeze, one of the world's foremost hydrogeologists, penned this "allegory" several months later in 1987:
Freeze is telling us not to take this too seriously, which is good advice.
If you are still reading this, you're no doubt wondering, "Does this guy have too much time on his hands or what?"
I suspect this post will generate more than the usual number of comments.
"And that, my children, is why 'ground water' is always two words, or one." -- Michael E. Campana