Why not "volume"?

relative Googlehits "amount/quantity/volume of water" - 216 Mio : 78 Mio : 86 Mio

Bei aller Vorsicht vor Google-Beweisen kann man zumindest daraus schließen, dass jede dieser Varianten schon mehrmals schriftlich verwendet wurden. (Und nein, ich habe nicht all Treffer auf Relevanz geprüft).

Ich habe auch mit Kontext gegoogelt:

https://www.google.de/?gws_rd=ssl#q=%22spraye... = 11000 hits
https://www.google.de/?gws_rd=ssl#q=%22spraye... = 34000 hits, und die sehen gut aus....

Volume is also good, but I used it to translate "Wasservolumen", and I do want to make a distinction with "Wassermenge"...

"quantity of water" sounds slightly more "technical" than "amount" I think; "drink large amounts of water (in very hot weather)" e.g.

I don't think "countability" is an issue here. Both words are countable here, and can be used in either the singular or the plural:

They drank a large amount of water.
They drank large amounts of water.
They drank a large quantity of water.
They drank large quantities of water.

In any case, you should not say "water quantity" or "water amount", but rather "quantity of water" or "amount of water."

Volume is also good, but I used it to translate "Wasservolumen", and I do want to make a distinction with "Wassermenge"

In your document, do "Wassermenge" and "Wasservolumen" actually refer to the same thing? If they do, you can/should use the same word/phrase to refer to them. If there's a difference, though, differing words are called for.

In technical writing, consistency is important. Many German technical documents that I work with, however, use inconsistent terminology. Sometimes it's due to sloppiness on the author's part. Often, though, I get the impression that its due to the "rule" that some teacher pounded into the writer's head at an early age, saying that you should never repeat a word in a sentence/paragraph (and sometimes it seems like they try to achieve that per page, or even per document). Technical documents are not novels or poems!

That side, I agree with #4 & #5 if you want to avoid volume. The "of" construction is definitely more colloquial in English than the more "Germanic" word order.

AE hier.

Hopefully it's obvious to everyone that #6 made a typing error in his final sentence: "That side, ..." = "That said,..."

My comment:

In colloquial English #5 mentioned

"They drank large quantities of water."

I just want to stress that we do indeed often say large quantities as well as large volumes in the plural. When I think about it, it does sound rather illogical, but so be it.

I advise against volume(s) of water.

I like a large amount of water.

A bit more casual: They drank a lot of water/lots of water.

From the OP: It is regarding the water volume to be added to the tank of a sprayer...

A complete sentence can only help, but seeing how there isn't one, maybe something like:

Add small quantities/amounts of water (whenever) ... (it also depends on how formal you want to be - "quantities" is a bit more formal than "amounts." IMO). And I agree with those advising against "volume" in this context.