Thirsty? Which water bottle is the safest and cleanest to drink from?
Alysha Lee
Sir Winston Churchill Secondary
Floor Location : J 175 H

Have you ever wondered if your water bottle is clean after you constantly drink from it? Reusable water bottles are an essential part of everyday life.
I often wondered whether the fancy stainless steel or glass water bottles were cleaner and safer than the plastic one that I am using. I hypothesized that….if I drink from the three different water bottles: stainless steel, glass, and plastic and swab the inside of the drink container and then onto the petri dishes to find out how many bacteria colonies will form, then the stainless steel container will produce the least number of bacteria, because it provides insulation, keeping the water cold so that it prevents bacteria from growing, and the smooth inside surface makes it harder for the bacteria to adhere.
For my experiment, I tested the cleanliness of a glass, plastic, and stainless steel water bottle. Each water bottle was washed thoroughly and then filled with 500 mL of purified water. I drank from each water bottle 3 times daily on a rotational basis for 5 days. With a sterile swab, I took samples from each bottle by swabbing the inside of the drink container and onto a petri dish. Samples were taken on Day 0, 2, 4 and 6, with Day 0 samples as the control group. I incubated the petri dishes for six days and observed them daily. I repeated this experiment two more times by following the same procedure.
My results showed that both the stainless steel and glass water bottles had a tremendous number of bacterial colonies growing on the petri dishes over the course of six days. The plastic reusable water bottle on the other hand had the least growth. Closer to the “Day 6” swab though, all the water bottles seemed to have a great amount of growth that I was not expecting to see. I observed that after 2 days of incubation, the plates were the most reflective of the number of bacteria in each bottle because the bacterial colonies had just started to grow. I also contacted a Medical Microbiologist that found that most of the bacteria from the samples were gram-negative bacilli (rods) bacteria. These gram-negative bacteria are commonly found in wet environments and can cause serious illness in people with a weak immune system.

From this experiment I have come to the conclusion that my hypothesis was incorrect. The stainless steel water bottle had the most. This may be because the stainless steel creates an environment inside the water bottle that allows the bacteria to thrive and multiply quickly. Glass is also not a suggested option because it also has an abundant number of fast-multiplying bacteria. Compared to the other two bottles, the plastic water bottle had the least number of bacteria inside. Even though the plastic water bottle was the safest in comparison, it still contained bacteria. Therefore, all water bottles should be washed daily and thoroughly (e.g. in a dishwasher) to keep your water clean and safe to drink!