Perfect: It's sturdier than a milk carton, so it should last a long time. First, I washed it out very thoroughly. I put 1/4 cup of baking soda in it and filled it with hot water, and let it sit overnight to try to make sure it gets completely cleaned out. I would hate to kill all my plants from a touch of Downy in the water I put on them!
Next, I took a hammer and a thick nail and put some holes in the lid.
See that hole in the handle? that's important for air, otherwise your water will not come out of the can. Feel free to put two or three air holes in the top of the handle, approximately at the part where the inside of the handle attaches to the bottle.
Now to test it out!
It's not perfect, but it's a watering can for free. I think it's a lot better than paying ten bucks for a glorified bucket. My neighbors probably think I'm crazy and pouring chemicals on my plants....