The most common and most likely answer to this crossword clue is the 8 letter word SPRAYING
I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Watering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case watering = spraying.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
SPRAYING verb- To project a liquid in a dispersive manner toward something.
- To project in a dispersive manner.
- To project many small items dispersively.
- To urinate in order to mark territory.
- To allocate blocks of memory from (a heap, etc.), and fill them with the same byte sequence, hoping to establish that sequence in a certain predetermined location as part of an exploit.
- The act by which something is sprayed.