Findings and Explanations
Metal bottles are capable of maintaining their temperature, as well as limiting light intensity in the bottle. So they will not cultivate any excess bacteria at the start. Usually the bottle mouth has a rubber seal and is larger than the bottled water ones. Therefore bacteria is not able to enter easily. Though, when water is drunk from the bottle, saliva which contains bacteria is able to enter. Over time the bottle will be at room temperature, allowing the bacteria in the water grow. This will make the bottle have an increased rate of bacterial growth, such that they have the fastest growth rate of bacteria.
Plastic bottles are often translucent and allow some light to travel through its plastic material. This makes sure that the UV light found in sunlight does not kill off most of the bacteria. Because of their usually large bottle mouth and large plastic frame, they can allow the temperature inside the bottle to be the same as the room temperature. They can also be difficult to close tight and usually have sufficient warmth and space in the bottle for bacteria to grow. Thus, they have the most bacteria found in them throughout.
Recyclable bottles, the ones that are bought with bottled water, often have a thin material for the body. This allows sunlight to enter the bottle easily, killing off some of the bacteria. They all have a small bottle mouth, which allows the bottle cap to be closed tightly. It also ensures minimum contact with outside air and bacteria. However bacteria from the mouth can easily find their way in. The temperature of the bottle will be at room temperature most of the time. This allows the bacteria in the water to grow, but to a certain extent. Thus, they are second for the bacterial growth, as well as the growth rate of bacteria.