I've been following the Cookie Tin water heater thread with great interest and had planned to make one, however cookie tins are scarce in my neck of the woods. That may be hard for some to believe, but there are no usable cookie tins within an hour's drive, a two-hour round trip. The only one I found was an "antique" at a thrift shop 14 miles away, but it was too small — and 6 bucks! No sale. So, I made a heater out of scrap pressure-treated 2 X 4s and new cement backer board, which was readily available only 15 minutes away. I settled on a 12'' X 12" exterior, which provided a 9" X 9" interior (minus a half inch for the backer board thickness). In addition to the wood scraps, I already had in my possession a used lamp socket and lamp thread, light bulb(s), 18 ga. electric cord, screws, masonry cutting wheel, and dust mask. My only expense for this project was a sheet of 1/4-inch thick, 36" X 60" cement backer board, which was $11.65 out the door. By the way, cement backer board is fireproof and nonconductive. I tested the unit last night, when the low temperature reached 22 F. I had placed one bowl of water on the heater, which was equipped with a 60-Watt bulb, and a second bowl on the porch railing; both were 100% outdoors. I checked them this morning just before dawn: The second one had frozen solid, while the heated one remained liquid at a temperature of 75.5 F. That's nice and warm, and therefore unnecessary, so I will test again with a 40-Watt bulb tonight, then again with the actual chicken waterer, which was frozen this morning (not the reservoir, just the bowl portion). I have applied Thompson's Water Seal to the exterior in the hope that the unit may be easier to clean in the event my birds make "deposits" on it. Here are some pics, and if anyone has any questions, please feel free to ask.