One reason is that the plastic component of your water bottle can begin to degrade. The last time I noticed this was when my partner’s water smelled like onions. The problem became worse with age, and the only solution was disposable replacements at full price. Over time, plastics break down into smaller pieces called “plasticizers.” According to Dr. Joseph Mercola (a biochemist, pediatrician and osteopathic physician with over 20 years of surgical experience), some plasticizers are estrogenic; others can cause allergic reactions or disrupt our endocrine system — leading to things like cancer, diabetes or ADHD-like symptoms in children.*