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I'm currently looking at using colored see-through water bottles. Mold is green because it reflects green light, so I have a theory that a green bottle would grow the least amount of mold because it only allows green light through which the mold can't absorb.

So does bottle color make any difference on mold growth? If so, is it worth it to look specifically for green bottles?

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    Maybe you are confusing mold (which is a fungi, often white but also green and red are common colors, grows in the dark) with algae (usually green, but can be also blue, needs light to grow). Either of these can grow in a water bottle, and you can also get a bacterial colony started (often colorless or whitish film, bad smell, grows in dark).
    – jpa
    Commented Aug 8, 2019 at 7:36

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Mold doesn't need light to grow, in fact it thrives in darker environments. It needs warm temperatures, water, and food (sugars/salt from backwash). So those three things are independent of water bottle color.

As an aside, in terms of light filtration, a green water bottle isn't a perfect green light filter. So while it will have some effect on the color spectra of light passing through, it won't be the same as say a green filter for imaging.

In summary, the color of your bottle won't affect mold growth. Just make sure to clean it well (scrub with a toothbrush or similar) and sterilize (boiling water) every once in a while (Ideally ~1/week).

I can also unfortunately say from experience that green water bottles can indeed have mold grow inside them.

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  • Does it just thrive in darker environments because these tend to be more moist, or is it inherently light-averse?
    – leftaroundabout
    Commented Aug 8, 2019 at 9:44
  • Mold is highly susceptible to UV radiation. Dark locations have less UV (from the sun).
    – dwizum
    Commented Aug 8, 2019 at 13:59
  • Moreover, with a clear glass bottle, it will be far easier to see if there is mold growing inside it. The more opaque the bottle, the harder it is to tell if there's something nasty going on inside it...
    – Darrel Hoffman
    Commented Aug 8, 2019 at 20:47
  • While mold doesn't need light to grow, it doesn't mean that all types of mold (or fungus) are insensitive to light. There might very well be some species that are damaged by visible light (I don't know, but it's possible).
    – CJ Dennis
    Commented Aug 9, 2019 at 5:02
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Mould does not need light to grow, and the proposed green colour will prevent you seeing mould growth, and being darker inside, will encourage mould growth.

What is important for mould growth is damp conditions.

The solutions to the mould problem are

  • Sterilize the bottle regularly.

  • Drain the bottle upside down after emptying or cleaning.

  • Store the empty bottle dry inside.

  • Leave the cap off the bottle when in storage.

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@noah is correct but I want to add:

  1. UV in sunlight can actually kill the top layer of mold and mold spores. But it won't do much to established mold. Having a dark colored bottle will actually increase the chances of mold developing because you're blocking UV.

  2. Bottles are darker colored in industries like pharmaceutical and cosmetics to block UV rays which will break down vitamins and cause or speed up other unintended chemical reactions. In these industries various things are done to reduce the amount of mold like using very clean water and manufacturing processes and introducing additives.

"[C]ontainers in amber, cobalt blue and vintage green offer UV protection for beauty, food and beverage products with sensitivity to light. Each of these colors provides differing levels of UV protection: Amber, high; Cobalt, medium; and, Green, minimal." glass now

"The range of 200 to 280 nm UV light spectrum (UV-C) has a germicidal effect on microorganisms, including bacteria, yeasts, molds, and viruses. Microbial inactivation in liquid foods by UV-C depends on optical and flow properties of the product..." science direct

"UV light killed microbes growing in the cooling systems, causing a 99 percent reduction in the concentrations of bacteria, fungi and endotoxins, which are irritants produced by mold" Sick Building Syndrome fixed with UV

"Mold is caused by lingering moisture in dark place... check areas that are hidden, damp and dark because sunlight is the best anti-mold too." mold remediation

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