A pump possibly collecting last of water on land (6)
I believe the answer is:
ashore
'on land' is the definition.
('ashore' can be a synonym of 'on land')
'a pump possibly collecting last of water' is the wordplay.
'pump possibly' becomes 'shoe' (pump is a kind of shoe).
'collecting' means one lot of letters goes inside another.
'last of' suggests the final letters.
The last letter of 'water' is 'r'.
'shoe' placed around 'r' is 'shore'.
'a'+'shore'='ASHORE'
(Other definitions for ashore that I've seen before include "On land (as opposed to the sea)" , "on terra firma" , "On(to) dry land" , "Aground" , "Off the boat" .)