Doubts in providing power to an LED
Your 9V source is coming from something (probably a switchmode AC adapter) that has some "leakage" from the mains to ground. 

You can likely solve this by grounding (to earth) one side (usually the minus side) of the adapter DC output. This is also an improvement from a safety point of view, especially if your AC adapter is dodgy. Since water is involved it becomes even more important. 







simulate this circuit &ndash; Schematic created using CircuitLab

Typically there is a "Y" safety capacitor from the mains to the output inside the AC adapter which causes some current to flow.