Hello. I've wondered this myself and finally found out after chancing upon your question. The short answer (plus caveat) is yes, as long as you wash it in-between uses with hot, soapy water and allow it to dry. Why? According to about.com:
- Bacterial Concerns for All Water Bottles: The real culprits for the safety of reusing any water bottle are the bacteria and fungi that can grow in damp or partially full bottles once they have been opened. These bacteria generally come from your hands and mouth, or any dirt that comes in contact with the mouth of the bottle.
Below, is another relevant segment from plasticinfo.com which supports this conclusion.
- When consumers choose to refill and reuse convenience-size plastic bottles, should they be concerned about potentially harmful bacteria?
Not if they clean their plastic bottles between uses just as they would other drinking containers. Plastics are by nature extremely sanitary materials, and plastic bottles are no more likely to harbor bacteria than other kinds of packaging or drinking containers. Bacteria thrive in warm, moist environments. Once bacteria have been introduced, virtually any drinking container (coffee mugs, drinking glasses, serving pitchers, etc.) becomes a suitable environment for bacterial growth. - Consumers should clean any drinking container with hot soapy water and dry thoroughly between uses. Bottles specifically designed for extended reuse are often made with wide openings that allow consumers to use cleaning instruments and easily dry them.