2 biggest concerns about reusing bottles

Bacteria
There are two main health issues to keep in mind when considering whether to reuse water bottles. The first is the risk of bacterial contamination. Single use plastic water bottles, of the type most bottled water comes in, have very narrow openings which makes them difficult to clean. The opening can be so small that you can’t fit a brush into the bottle to clean the bottom and sides. Over time, if you reuse water bottles, bacteria can build up. The plastic in single use water bottles can also develop small cracks after repeated use providing a place for bacteria to hide and contaminate the water. These bottles also don’t hold up well to the temperature of a dishwasher and the heat can cause further cracking and damage to the bottles.
Leaching
The second health issue relating to the reuse of plastic water bottles is the potential for plasticizer to leech into the water. If single use plastic bottles are washed in warm water, it can hasten the breakdown of the plastic fabric and lead to leeching of chemicals
into the water. There’s increasing concern about this particular issue with some experts saying that plastic bottles are unsafe even for single use. It’s believed that these bottles may set around in warm warehouses where the heat could cause chemicals to enter the water even before they reach store shelves. The chemical of concern, known as bisphenol A, is believed to alter the levels of certain hormones in the human body which may increase the risk of certain types of cancer, particularly breast and prostate. Bottles made of polycarbonate, marked with a number seven, are at the greatest risk of leeching bisphenol A.
Are There Safe Alternatives?
Rather than reusing water bottles, a safer solution may be to buy a stainless steel water container for carrying water to and from the gym. These bottles, found in the camping supply section of stores such as Walmart are believed to be safe and are easy to care for and clean. They’re a nice alternative to plastic.