Had a quick look at water on deck, not cold but rising (6)
I believe the answer is:
peeked
'had a quick look at' is the definition.
'water on deck not cold but rising' is the wordplay.
'water' becomes 'pee' ('pee' can be a synonym of 'water'**).
'on' is a charade indicator (letters next to each other).
'not' suggests deleting specific letters.
'cold' becomes 'c' (eg on taps).
'but rising' says the letters should be written backwards.
'deck' with 'c' taken away is 'dek'.
'dek' reversed gives 'ked'.
'pee'+'ked'='PEEKED'
(Other definitions for peeked that I've seen before include "Glanced surreptitiously" , "Looked furtively" , "Looked surreptitiously" , "Took a secret look" .)