Green’s Dictionary of Slang

(Aus. Und.) a counterfeit banknote or cheque.

1900–10

Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 28: BRIDGE-WATER: thieves slang Australian. An imitation or forgery either of a bank note, cheque, or other promise to pay [...] General meaning – any letter, jewellery or other article used for fraudulent purposes is alluded to as a bridge-water.