What is Recycling Code?
Check the bottom of the bottle, there should be a triangle sign and there will be a number on it.
The plastic used in the beverage bottles contain a potentially carcinogenic element (something called diethylhydroxylamine or DEHA). The bottles are safe for one-time use only especially for those bottles with recycling code below 5. If you must keep them longer, it should be or no more than a few days, week max, and keep them away from heat as well. Repeated washing and rinsing can cause the plastic to break down and the carcinogen (cancer-causing chemical agents) to leak into the water that you are drinking.
While it's true that many plastics are imprinted with a numeric code. Like all materials intended to come in contact with foods or beverages, the plastics used as beverage bottles are subject to federal safety review and regulations. Such materials must meet stringent U.S. Food and Drug Administration safety standards before they can be marketed to consumers.
So, what is in the number? The numeric codes that you see on many plastic items are used to help sort port-consumed plastics for recycling purposes. Different types of plastics are sometimes referred to as "resins" and the numeric symbols are known as "Resin ID Codes".
Each number (1 through 6) signifies a specific type of plastic and usually appears inside a small triangle imprinted on the bottom of a plastic item. The number "7" is used to represent a group of other plastics or combination of plastics.
Hence, the numbering is just meant to differentiate the type of plastics for recycling purpose.
1 - PET, polyethlyene terephthalate
2 - HDPE, high-density polyethylene
3 - PVC, polyvinyl chloride
4 - LDPE, low-density polyethylene
5 - PP, polypropylene
6 - PS/PS-E, polystyrene / expanded polystyrene
7 - OTHER, resins or multi-materials