When buying bottled water, consumers are advised to check the bottom of the bottle, in order to protect their health. Plastic bottles labeled with letters like HDP, HDPE, PP and a few others, do not release any toxic material in the water, and the remaining letters can represent the chemicals…
Source: You Need to Know This Before Buying Bottled Water
So important that I will include the text here.
A Complete Guide to Plastic Bottle Safety

1. PET or PETE:
This one probably sounds familiar. It is the most commonly used plastic material in packaging and consumer products, used especially for water and soft drink bottles. This kind of plastic is only intended for single use and is difficult to decontaminate, meaning that repeated use can be harmful. The more you use it, the higher the risk of leach and bacteria. Also, the metals and chemicals released by this material may tamper with our body’s hormonal balance.

2. HDP or HDPE:
HDPE is a harder type of plastic often used for milk jugs, detergent bottles, oil bottles, toys and some plastic bags. Experts claim that this is the safest kind of plastic that you can choose when buying bottled water, because it barely releases any chemicals. This means your water will be cleaner, hence causing minimal harmful effects on your health

3. PVC or 3V:
This symbol indicates the use of PVC, a highly toxicplastic that is soft and flexible, and is generally used for food wrapping, oil bottles, teething rings, toys, and blister packaging. The chemicals it releases are said to have serious consequences on our body, since they pose effects on our hormones. Experts suggest to avoid packaging made from the PVC and try to find an alternative to it.

4. LDPE:
Although this type of plastic does not release chemicals into the water, you are unlikely to see this label on your water bottle, because the LDPE material is not used in its production. Rather, you would find it in food packaging, in the case of which you should still try to avoid it. LDPE may still release highly dangerous chemicals in the foods you eat.

5. PP:
Yogurt cups and syrup packing are made of this white-colored or semi-transparent type of plastic, referred to as PP (polypropylene plastic). This kind of material is tough, lightweight and heat-resistant. This material won’t melt easily if heated. Overall, it is a rather safe type of plastic, and it can also block out moisture, grease and chemicals.

6. PS:
PS stands for Polystyrene – a type of inexpensive and lightweight plastic that is used for a range of products. We have often used this type of plastic for disposable styrofoam drinking cups, egg cartons, plastic picnic cutlery, and take-out “clamshell“ food containers. PS should be restricted to short-term usage only, since dangerous carcinogenic substances could be released from it when heated.
7. PC or non-labeled plastic:
This is potentially the most dangerous plastic found out there. If you ever find the “PC” label on plastic bottles (or no label at all), make sure you steer clear of it as much as possible. It refers to a catch-all category for polycarbonate materials and “other” plastics, which contain chemicals that are likely to leach into the food or drink products it makes contact with. Examples of the use of this material include sports water bottles and food containers. It is highly discouraged to reuse or recycle this type of plastic.
Note: These kinds of plastics are not only used for food and drink products. We also find them in everyday items in which they may not directly affect our health, such as water pipes, signs, clothing, furniture, shower curtains, textiles, stationery, insulation, diapers, medical equipment, etc. Nonetheless, we should always be knowledgeable about the materials and chemicals included in the products we buy, taking extra care on the ones that contain food and drinks.