Reusable plastic bottles have a nasty habit of harboring an E. coli bacteria known as coliform if they’re not properly cleaned. Wide-mouthed bottles are the easiest for cleaning, and the harder the material your bottle is made out of, the better. – Scratches in the service provide a great space for bacteria to thrive. Wash and dry both completely and regularly – it’s also suggested that you soak your bottle in bleach water once weekly.
Source
