So, how long has this information been out there? In terms of how long it's been on Aldi's packaging, we really can't say, but evidently this corn-popping tip has been around for over 10 years. One user of the Straight Dope Message Board posted in 2009 stating that their store-brand bag of microwave popcorn gave this same advice, and was asking why water would help the corn pop faster or better or whatever it's supposed to do.
They received several possible answers, one of which read, "The internal parts of the microwave cooking compartment (walls, floor, door, turntable dish) won't need to heat up when you go to heat up the popcorn, and that makes the process faster and more consistent," and another that explained, "Boiling the water makes steam, the steam/vapor remaining in the oven when you pop the popcorn is more efficient at transferring heat evenly to the popcorn, and helps temper cold spots in the microwave."
There's also a tip for reheating pizza in the microwave that calls for putting a glass of water in along with your leftovers since it somehow sucks up the excess microwaves. Since Aldi recommends removing the water before putting in the popcorn, that excess microwave thing probably isn't the reason the popcorn hack works. Still, the point is that it evidently does work... well, maybe.
