I've always heard not to re-use disposable plastic water bottles.

According to this Huffington Post article, the reason is because:

everyday wear and tear from repeated washings and reuse can lead to physical breakdown of the plastic, such as visible thinning or cracks. Bacteria can harbor in the cracks, posing a health risk.

Also, a study from the Canadian Journal of Public Health found nearly two-thirds of bottles sampled had bacterial levels that exceeded drinking water guidelines. (See here).

So my question is: What kinds of bacteria (or other microorganisms) live in water bottles? In other words, which species should we worry about in these cases?

This Livestrong Article lists species found in the water itself, but I'm more curious about what organisms get introduced and grow through re-use of the bottle.

This is relevant because bottled water just became the most sold consumer beverage in the US.

  • 2
    $\begingroup$ I usually follow the rule: reusable until perma-stank condition achieved. The water in your faucet is not sterile. It is host to many bacteria, molds and yeast. This is one contributor to contamination. Plus the air you breath is host to microbes, therefore opening the water bottle contributes to contamination. But, if you rinse and wash with soap between uses, it should be good for a few weeks before it's time to be recycled. $\endgroup$
    – Bob
    Mar 23, 2017 at 23:03

2 Answers 2


In addition to the cracks providing a better place for bacteria to grow, all plastic bottles, when reused, are subjected to high levels of bacteria due to contact with hands and mouths. So your water bottle can potentially host a range of bacteria.

Your water bottle traps humidity inside and provides a perfect growing medium, especially near the threads of the mouthpiece and along/within cracks in the bottle which provide better bacteria accumulation.

Microorganisms that Grow

  • Overall, most sources I could find remained very vague (numerous News stories) or mentioned bacteria generally:

  • Staphylococcus and streptococcus species, [Source].

  • Norovirus [Source].

  • The seemingly most detailed studies I could find came from Watanabe et al. 2014 and Ohnishi et al. (2012) who examined microbial growth in numerous beverage types. However, I could only find their their abstracts online, which report:

    • microbial growth was detected in ~20% of poured samples, and in ~51% of drank samples.

    • 225 bacterial strains, 27 mold strains, and 77 yeast strains were isolated

      • Bacteria: Streptococcus spp. (e.g., S. salivarius) and Staphylococcus spp. (e.g., S. aureus), made up the majority. Enterotoxin-producing S. aureus and Bacillus cereus were also isolated.

      • Molds: Cladosporium spp., Tramets spp., Bjerkandera spp., and Penicillium spp.

[I Will hunt down these articles to get more details and will update accordingly when I find them...]

Microorganisms in the Water

  • Based on a study found here, brand new bottles of water can have fungus spores (typically harmless), but opened bottles can show signs of greater diversity (e.g., fungi, skin Staphylococcus, and yeast.

  • Igbeneghu & Lamikanra (2014) found Staphylococcus species (notably S aureus) and strains of Pseudomonas in bottled water available in Africa.

  • Your Livestrong article lists a number of non-human pathogens such as: Ralstonia Pickettii, Acidovorax Temperans, A. Delafieldii, Agrobacterium Rhizogenes, Burkholderia Glumae, and Bacillus Thermoglucosidasius.

  • Juvonen et al.'s (2011) "Microbiological spoilage and safety risks in non-beer beverages" provides a thorough list of organisms found worldwide in different bottled waters and other beverages.

Other Issues

  • According to Rose State microbiologist, Dr. Amy Hurst:

The plastic materials degrade into the water, so then you're drinking very small plastic molecules. [Source].

  • PET plastics tend to leach when exposed to realistic though extreme conditions, such as exposure to sunlight, heat and storage time. [See UF article]

  • Bisphenol-A (BPA) and phthalates present in the bottles can leach into the water and possibly cause harm to humans.

  • Rochester (2013) provides a good review of BPA effects in humans and other test organisms.

  • New research shows that BPA alternatives such as BPS aren't any safer either; in fact, in some cases they are considered more dangerous to humans. All bisphenols are capable of mimicking the body's sex hormones, says Robin Mesnage, research associate with King's College London.

  • Al-Saleh et al (2011) found that 76% of the bottled waters they tested in Saudi markets contained measurable amounts of phthalates.

So Reusable Plastic Bottles are Better Right?

  • Well, from a bacteria standpoint, this isn't necessarily true. According to a small study of 12 reusable bottles being used for a week:

    • Avg bacteria load: 300k CFUs (colony forming units). Ranged between 25 - 900k CFU/cm$^2$.

    • Notable types found: E.coli, salmonella, and various gram-positive cocci and gram negative rod bacteria.

    • They found that different bottle types harbored different amounts and kinds of bacteria.


True enough the re-usability of plastic bottles is quite a problem even in the area I live. This is due to multiple factors; one of those factors is the symbiotic microorganisms that could be living in your mouth (from my lectures) as well as any contaminant from anything you've eaten$^1$. That however isn't the only thing that could be contaminating your water bottle. The exposure to the air itself may contaminate. (that's why in microbiology we use a laminar flow cabinet or work close to a flame).

That's also why hospitals have air purification systems to avoid infections$^2$.

As a result, the amount of possible contaminants are too big to list. We could list those that I personally think would be more relevant to list -- these include our mouth natural flora since saliva is the most common contaminant of reusable bottles:

  • lactobacilli;
  • Candida albicans;
  • enterococci;
  • Streptococcus salivarius;
  • Fusobacterium nucleatum;

List obtained from Almståhl et al.$^3$

Almost all of these microorganisms are associated with some sort of disease or another.

I didn't actually find any specific study on the reuse of water bottles so i apologize for not being capable of giving a more definitive reply.

Sorry if i have failed to answer your question in any way or have misinterpreted what was required, I hope my research was some help to you.


  1. (Mahvash Navazesh, DMD, Satish K.S. Kumar, MDSc1, Measuring salivary flow : Challenges and opportunities)
  2. (W.D. Griffithsa, A. Bennettb, S. Speightb, S. Parksb. Determining the performance of a commercial air purification system for reducing airborne contamination using model micro-organisms: a new test methodology.
  3. Almståhl A, Wikström M, Fagerberg-Mohlin B. Microflora in oral ecosystems and salivary secretion rates--A 3-year follow-up after radiation therapy to the head and neck region.
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    $\begingroup$ This is not a problem, but one of the strength of the stackexchange communities. People correct mistakes that happen. Welcome to biology, btw. :-) $\endgroup$
    – Chris
    Mar 23, 2017 at 16:40
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    $\begingroup$ Great answer here, +1 and I edited your other post - don't emphasize being a newbie. This style of answering is awesome and a lot better that the average user accomplishes here. $\endgroup$
    – AliceD
    Mar 23, 2017 at 22:01
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    $\begingroup$ @AliceD xD Had that happened to me i would totally learn to fear the community. I'm glad my teachers teach me properly!! $\endgroup$
    – Kiny
    Mar 23, 2017 at 22:18
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    $\begingroup$ @Kiny and that is exactly my biggest concern of harsh reactions to new users. People need to be given the freedom and help to find their way. $\endgroup$
    – AliceD
    Mar 23, 2017 at 22:19
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    $\begingroup$ Kiny - sometimes I still correct @AliceD's posts, 30k rep later (and even though I am relatively quite new) ;) $\endgroup$
    – Bryan Krause
    Mar 24, 2017 at 15:46

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