Wet on the day, thought the water isn’t settling (8)

'isn't settling' is the definition.
The answer and definition can be both related to change as well as being present participle verbs.
Maybe they are linked in a way I don't understand?

'wet on the day thought the water' is the wordplay.
I cannot really understand how this works, but
'day' could be 'd' and 'd' is found within the answer.
'water' could be 'rain' (rain is a kind of water) and 'rain' is present in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?