Lighters that need water (6)
I believe the answer is:
barges
'lighters' is the definition.
('barge' can be a synonym of 'lighter')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for barges that I've seen before include "Canal and river boats" , "Long boats on inland waterways" , "Broad flat-bottomed boats" , "Flat-bottomed boats for carrying loads" , "Inland waterway longboats" .)