Most inexpensive plastic water bottles contain BPA, which is a human endocrine disrupter, the glands that secrete hormones into the blood.  BPA is a chemical made from petroleum, the same petroleum that oil and gas are made of.  It mimics the body’s hormones, causing infertility problems, especially in women, as well as has cancer-causing tendencies.
Thus, stainless steel bottles are a healthy alternative.  Not only because they are made of a higher and safer quality, but they also keep cold drinks cold and hot drinks hot.  They are dishwasher safe, include a sport cap and spout, and reduce waste.