My Aeroponic plants give off a little static when touched during water flow.

I have a little aeroponic tower set up in my apartment, i transplanted some 2 week old lettuce and Pak choi plants into them yesterday. Today i set the system up, kept in my nutrients and recorded an EC of 0.7. I tried touching them whiles the system was active and felt them give off a little static shock. Cant find anything related to it online. Any idea whats the principle behind it,