water used in the membrane separation process

a similar German term used for chemicals is "Scheidewasser"

 aqua fortis | das Scheidewasser  Pl.: die Scheidewässer
https://dict.leo.org/englisch-deutsch/Scheidewasser

Salpetersäure (HNO3), genannt auch Scheidewasser, ist die bekannteste und stabilste Sauerstoffsäure des Stickstoffs. Die Säure wird seit 1908 großtechnisch im Ostwald-Verfahren durch katalytische Oxidation von Ammoniak hergestellt. Das Ammoniak wird zuvor mit dem Haber-Bosch-Verfahren aus Luftstickstoff und Wasserstoff hergestellt.
https://de.m.wikipedia.org/wiki/Salpetersäure

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Note added at 6 hrs (2022-04-28 16:06:07 GMT)
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Other English synonyms :

Nitric acid (HNO3), also known as aqua fortis (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid.
:
Nitric acid is the primary reagent used for nitration – the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.
:
The main industrial use of nitric acid is for the production of fertilizers. Nitric acid is neutralized with ammonia to give ammonium nitrate. This application consumes 75–80% of the 26 million tonnes produced annually (1987). The other main applications are for the production of explosives, nylon precursors, and specialty organic compounds.[17]
https://en.m.wikipedia.org/wiki/Nitric_acid