Endless mineral water to drink following illness and unpleasant discharge (8)
I believe the answer is:
effluvia
'endless mineral water to drink' is the definition.
I can't tell whether this definition defines the answer.
'illness and unpleasant discharge' is the wordplay.
I cannot really understand how this works, but
'illness' could be 'flu' (flu is a kind of illness) and 'flu' is present in the answer.
This explanation may well be incorrect...
'following' acts as a link.
Can you help me to learn more?
(Other definitions for effluvia that I've seen before include "Unpleasant discharges" , "disagreeable vapours" , "nasty exhalations" , "Nasty smells" , "nasty vapours" .)