Ground water versus groundwater

It has been a longstanding practice within the USGS to spell ground water as two words and to hyphenate when ground water is used as a modifier (e.g., ground-water hydrology). Ground Water Branch Technical Memorandum 75.03 issued just under 35 years ago specified that the two-word form should be used.

USGS has now decided to make a transition to the use of groundwater as one word. Reports submitted for approval after August 1, 2009, will be expected to use the one-word form. During the transition period, the one-word or two-word spelling should be used consistently throughout a publication.

To view the memorandum explaining the decision, go to USGS.