Most water bottle makers intend for their products to be single-use. But if you’re concerned about the environment, or need a container in a pinch, you’ve probably wondered if you can refill them. Whether or not this is safe depends on the plastic used.  Types of Plastic Bottles Most water bottle packaging will display a number printed inside a triangle to show what kind of plastic it is. That number can also help you determine how safe it is to reuse.  Here are two of the most common kinds of plastics found in water bottles. Polyethylene terephthalate (PETE or PET). If you see a “1” on your bottle, it means polyethylene terephthalate. This lightweight plastic is useful for water bottles and containers like sauce bottles, nut butter containers, and other food packaging. ‌ Concerns with type-1 bottles (PET plastics). The FDA has declared PET plastics as safe for single and repeated use.‌ But when these types of plastics are kept in extremely high temperatures, there is a risk of a chemical called antimony leaching. Still, chemical leaching risks are low when you store PET bottles correctly. It’s best to keep these bottles at room temperature and out of the sun to minimize any chance of any leaching.‌ High-density polyethylene (HDPE).  If your bottle displays a “2,” the plastic is high-density polyethylene (HDPE). HDPE is a more sturdy, durable plastic. This makes it a good material for detergent bottles, soap bottles, and gallon-size liquid containers. Concerns with type-2 plastics (HDPE plastics). If you happen across a water bottle marked with a “2,” you can reuse it as long as it’s washed well and not cracked or otherwise damaged. This type of plastic is a low risk for chemical leaching.  Chemical Leaching A common concern with reusing water bottles is chemical leaching. This is when chemicals from the plastic mix with whatever liquid you put inside. But with the right storage and type of plastic, this isn’t normally a concern with single-use plastic bottles. Plastic Bottles and Bacteria Growth Plastic bottles can harbor harmful bacteria, which is why most manufacturers recommend you use them only once. In truth, bacterial growth in water bottles is a much bigger concern than chemical leaching.‌ Bacterial growth can happen quickly from the ordinary use of touching your mouth to your bottle. Even unfinished beverages left at room temperature can have startling bacteria growth throughout the day. It’s best to reuse plastic water bottles sparingly and wash them thoroughly because germs spread so quickly. Additionally, wear and tear on the bottle from reuse can create cracks and scratches in the surface where more bacteria can grow. If you need to reuse a plastic water bottle, make sure to wash it properly first.