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According to a Duke University press release titled Replacing Coal with Gas or Renewables Saves Billions of Gallons of Water:

Water consumption – the amount of water used by a power plant and never returned to the environment – drops by 260 gallons per megawatt

Is it true that this water never returns to the environment?

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    Define "returns to the environment". Does steam entering the atmosphere count? If you are a physicist, you'd probably say yes, because it is still H2O and will rain out somewhere. If you are an environmentalist in a drought-stricken country, you'd probably say no, because it is no longer available to fill rivers and lakes, or nourish crops in your (local) environment.
    – Jack B
    Oct 24, 2019 at 17:55
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    We also need a definition of "never". Are they claiming the water will not ever wind up returned to the environment at any point in the infinite future? Does it count if the water is returns a hundred years from now? A thousand years? A million? Eventually the sun is going to expand to engulf the earth. Does that count?
    – plasticinsect
    Oct 24, 2019 at 18:19
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    @ventsyv ok, I see now, the manuscript defines "consumption" as "the difference between withdrawal and discharge volumes, reflecting losses due to evaporation, leakage, or recharge to the deep subsurface." Only the press release says "never returned to the environment".
    – DavePhD
    Oct 24, 2019 at 18:49
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    Actually more water is returned because coals contain some hydrocarbons ( "hydro"= hydrogen , oxidized to make additional water ). Admittedly anthracite type coals have very little hydrocarbon but they are not used in power plants.
    – blacksmith37
    Oct 25, 2019 at 0:40
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    the press release is nonsense (megawatt substituted for megawatt hour), read the manuscript instead. iopscience.iop.org/article/10.1088/1748-9326/ab4d71
    – Jasen
    Oct 26, 2019 at 9:42

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If I'm allowed a little pun on this, it seems the press release uses an America-first definition of environment.

This is a study of water use for power generation in the US.

Despite the shift in source of energy generation, a majority of electricity generation in the U.S. still derives from watercooled systems. Approximately 40% of the total water withdrawn in the U.S. is used for cooling thermal power plants.

Pun aside, the point of the paper is to study how the (local) water supply gets stressed locally by electricity production. And the study does so at sub-national granularity actually.

enter image description here

Figure 3: Map of water scarcity and coal and natural gas plants. The amount of 2016 net electricity generation attributed to dry, once through, and recirculating cooling processes for natural gas and coal, sorted by the water-stress status of the plant location in the U.S. (A), and the proportions of generation within each category (B) (2, 3, 14). Colors within each bar show how much of the net generation took place in water stressed areas. In 2016, almost all generation using dry cooling applied for natural gas plants, while a majority of generation using once through cooling applied for coal plants.

As far as I can tell, the paper doesn't bother at all to model or even mention where the water [that power plants use] "ends up", i.e. there's not even a quantification of the immediate fate of the water used for cooling, after it leaves the power-plant site.

Also, the paper itself, unlike the press release, never even uses the word "environment" (well, outside the journal name and citations).

So, the press release used a weirdly narrow definition of "environment" (in that "return" statement) by which they basically mean the conventional source(s) of water typically exploited, i.e. "aqueducts".

Water stress index levels were taken from the Aqueduct Water Stress Projections from WRI [...]

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