Great idea to use an Aquarium heater as a heat source. They are watertight by default and way less expensive. I just need to adapt this idea for my ducks as they won't use nipple waterers.
I like to have multiple waterers for my birds and this is an excellent option for a second waterer for the cold weather! You never know when any option that uses electricity will fail and this seems like a good backup plan to what I already have. Thank you for the well written article!