Hi S.!
This sounded a little over the top to me. I have family in the medical industry and I've known pediatricians all my life. Never once have I heard of the plastic leaching into bottled water so much that it makes it unsafe. Now a bottle in an oven heated to 400 degrees, the plastic will begin to break down and melt at that point. Texas may seem like it, but it is nowhere near that hot!
So I searched for 'plastic bottle' on snopes.com, thinking you may have read this somewhere on the internet and believed it. It turns out that it is false. A college student wrote about this for his master thesis which was never subject to peer review, meaning no other scientific tests ever concluded that heated bottles were unsafe. In fact, it was tested and concluded to be SAFE before, and again after the media reported on the student's paper. This kind of stuff is passed around quickly because it scares people. Please read this link if you would like more info, and in the future, if something sounds fishy, do a search on snopes.com. I love this site! They have thousands of people on staff to research and figure out if things are true or false, and it can save you a lot of worry.
http://www.snopes.com/medical/toxins/petbottles.asp
I understand you are a single mom and you are trying very hard to be on top of everything. You are doing a great job! Try to make sure you are worried for a good reason though. In other words, don't sweat the small stuff. =)