All plastic products should have a recycling number from 1-7 inside a small triangle which is usually found at the bottom of the product.
The problem with plastic made products is that they can leach chemicals into your food/liquid, and it's these foreign chemicals that are called xenoestrogens which mimic the female sex hormone estrogen. However, because these chemicals are foreign to the body, they are far worse to our health than the estrogen that our bodies produce naturally.
To be sure that the product you buy does not leach, check the recycling symbol. If it is a #2 HDPE (high density polyethylene), or a #4 LDPE (low density polyethylene), or a #5 PP (polypropylene), it is fine. Plastic water bottles for example are usually a #1, and that means they should only be used once and then thrown away appropriately. Your better off using a water bottle (usually a #4 or #5), and filling it with your own filtered water from home.
Just google 'xenoestrogens and plastic' for more information.