The most common and most likely answer to this crossword clue is the 8 letter word IMMERSED
I've seen this crossword clue in The Times
I
M
M
E
R
S
E
D
More clues leading to the result IMMERSED
Buddy explains!

The straight part
We know that "Put in water" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put in water = immersed.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.
What does IMMERSED mean?
IMMERSED verb- To put under the surface of a liquid; to dunk.
- To involve or engage deeply.
- To map into an immersion.
- Under the surface of a liquid; sunk.
- Deeply involved.