Adds water to so called cover charges (8)

I believe the answer is:

hydrates

I'm a little stuck... Click here to teach me more about this clue!

'adds water to' is the definition.
(I've seen this in another clue)

'called cover charges' is the wordplay.
'called cover' becomes 'hyd' (I can't justify this - if you can you should give a lot more credence to this answer).
'charges' becomes 'rates' (rate is a kind of charge).
'hyd'+'rates'='HYDRATES'

'so' acts as a link.

Can you help me to learn more?

(Another definition for hydrates that I've seen is " Combines with water".)

I've seen this clue in The Sunday Times and The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.