How does algae form in water bottles?

Algae are a group of photosynthetic organisms, they are diverse group and can vary from single celled (microalgae) to multicellular forms (large seaweeds). read more

The water might contain microalgae, which need nutrient rich water and sunlight for survival and replication. (NRDC: Bottled Water) So, if the bottle is exposed to prolonged periods of sunlight, there is a good chance of seeing a rapid increase/accumulation of algae. read more

Of course the second component of your issue is the water. Most likely the water that was put into the bottles was not sterile or during the process of putting water into the bottles The contamination was picked up during the flow process of injecting the water into the bottles. read more

The mold was swirled inside a container of ice water until the agar formed a bottle. Just a few more minutes of refrigeration, and the bottle was ready for use. The algae bottle retains its unique shape until it is empty, and then it begins to break down. read more