Best definition
water rat
Derogatory Australian slang for a ship’s prostitute. A female who hangs around the commercial waterfront selling sexual favours to sailors,

usually ship’s crews from cargo vessels.

Susie is a water rat. She has been locked up by the vice squad at least six times.
water rat: define #2
water rat
often mistaken for a puddle of water, water rats are aquatic mammals which can be found in the ocean, sewers and school changerooms.

They are extremely violent so if you see one, experts recommend to run away like a girl.
dude 1: theres water right behind you

dude 2: WHAT?? *runs away like a girl*

dude 1: wtf

dude 2: soz i thought u said WATER RAT
water rat: define #3
water rat
a ruffian who who can be seen around the waterfront
If you hang around with that water rat too much and you’ll wind up in jail with him.