Waterside dump in London (10)
I believe the answer is:
shoreditch
'in london' is the definition.
(area of London)
'waterside dump' is the wordplay.
'waterside' becomes 'shore' (eg the sea shore).
'dump' becomes 'ditch' (both can mean to discard).
'shore'+'ditch'='SHOREDITCH'
(Other definitions for shoreditch that I've seen before include "part of London" , "Area of east London" , "London district" .)