Green’s Dictionary of Slang

waterworks n.

1. [mid-19C+] tears.

2. attrib. use of sense 1.

3. [late 19C+] the urinary organs; also attrib.

4. [1910s] the vagina.

5. [2000s] one who weeps, a ‘crybaby’.

In phrases

turn on the waterworks (v.) (also turn on the main)

[mid-19C+] to start crying; turn off the..., to stop crying; also var. turn off the faucet.