Piezoelectrics could easily generate enough V to power LEDs using water
pressure and a mechanism to pressure-pulse the piezo element.
Wiring would still be required,though.(unless you consider printed circuit
boards to not be "wiring".


Maybe it uses a little turbine electrostatic generator? Kirby vacuum cleaners
use this method to power an LED in the powerhead to indicate brush speed. It is
just a copper strip contacting a plastic shaft.

--
Dennis