Might that be still belonging to me, a trawler at sea? (7,5)

I believe the answer is:

mineral water

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'might that be still' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'belonging to me a trawler at sea?' is the wordplay.
'belonging to me' becomes 'mine' (I've seen this before).
'at sea?' is an anagram indicator (I've seen 'at sea' mean this).
'a'+'trawler'='atrawler'
'atrawler' anagrammed gives 'ralwater'.
'mine'+'ralwater'='MINERAL WATER'

Can you help me to learn more?

(Other definitions for mineral water that I've seen before include "Drink with natural salts" , "Still or sparkling?" , "Sparkler" .)

I've seen this clue in The Telegraph.

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