Pass water round mine, on descent (8)
I believe the answer is:
pedigree
'descent' is the definition.
('pedigree' can be a synonym of 'descent')
'pass water round mine on' is the wordplay.
'pass water' becomes 'pee' ('pee' can be a synonym of 'pass water').
'round' indicates putting letters inside.
'mine' becomes 'dig' (I've seen this before).
'on' becomes 're' ('on' can be mean 'with reference to'**).
'dig'+'re'='digre'
'pee' enclosing 'digre' is 'PEDIGREE'.
(Other definitions for pedigree that I've seen before include "Lineage, ancestry" , "(Distinguished) lineage" , "Blood line" , "Stock" , "Breeding; descent" .)