Hippie yupsters have always been like, "I don't use plastic water bottles cause their chemicals cause cancer," or whatever, and we just laugh at them, but it turns out those people are the ones with the best erections.
BPA, a chemical found in like every plastic thing ever made and which you guzzle in your body every time you eat or drink from a plastic container, has been found to make men much exposed to high amounts of it much more likely to suffer erectile dysfunction.
So all those people with their fancy Sigg water bottles were right! Except Sigg water bottles were also full of BPA up until a year ago. Still, look for a dude driving a Volvo with an attached bike rack if you want a good, hard penis.