It's been said but here's a break down of what the numbers on the containers mean and what they are ok for, heating plastic is BAD this included heating in a dishwasher, which is how most of us sanitize bottles now, glass bottles are by far the best alternative. but here ya go.
number's 2 (HDPE high density polyethylene), 4 (LDPE low density polyethylene), and 5 (PP polypropylene) are considered safe for general use (not heating). 1 (PETE or PET Polyethylene Terephthalate) is considered safe for one time use (purchased water bottles) 7 are bottles containing BPA.
and here's some info on the effects of BPA
"Exposure to phthalates has been linked to cancer, infertility, premature breast development in girls and genital birth defects in boys. Young children can be exposed to phthalates by chewing on plastic toys, or through skin contact with lotions and shampoos that contain them.
Bisphenol A (BPA) is used to make hard, clear, polycarbonate plastic baby bottles and other containers. It is also used in dental sealants and in the lining of food and beverage cans. BPA mimics the hormone estrogen, and may interfere with brain-cell development, as well as with biological processes that rely on estrogen, such as ovulation and reproduction. Studies have shown that BPA leaches out of polycarbonate containers and metal cans, and have linked exposure to BPA to cancer, impaired immune function, early puberty, obesity, diabetes, and hyperactivity, among other problems."
and here's a link that goes over the different brands and gives saftey info. http://zrecs.blogspot.com/2007/07/z-report-bisphenol-in-p...
hope this can tell yo what you wanted to know take care.