Not my belief, but I caused it.
I work at an after school care centre. There is a water cooler in the room, which is available to children, staff and other adults to use whenever they want. It's a standard model with a little container under the taps to catch any water. It needs to be emptied every now and again.
One child was pushing the lever on the tap, just to fill up the container, so I told him that if the container gets too full and overflows, it gets into the electronics of the dispenser. Because we were in an old building, the electrical system wasn't that great, and the water would go from the cooler to the circuits, knocking out the power to the whole building.
The child backed away immediately! I can't believe I made it up on the spot.
A childhood belief about drinks

others believed things like this
- One day when I was 6 I learned that the toilet was NOT a water cooler. :/— J.C.
- when I was little, I used to think that everyone was a child but someone invented adults to take care of us.— chocolate
- I thought that hydrogen was pure water (since I knew hydro- meant water) and H2O was impure some how— Hexetic
- I used to believe that if i splashed water on the wall during a bath, the water would turn into spiders— justin
- I used to think that when the power goes out, the water also stops working.Anon
- that bathroom tap water was recycled "potty" water from the toliet. — livingdeadgirl