Black mold is a common fungus that accumulates in wet environments, such as damp walls and reusable water bottles. It rarely causes severe health conditions, but it is best avoided nevertheless. Black mold is associated with sneezing, coughing, congesting, asthma, and eye irritation. When you see black mold safe choices of response include departing the area, disposing of the moldy object, or cleaning the mold off the object.
Unlike commercial beverages, refillable water bottles are unfortunately easy for black mold and other pathogens to continually reinfect. Even if you filter your water with a purifier, the fact that you have a surface that is often wet and unrefridgerated, produces essentially a petri dish for mold.
Despite what various tutorials recommend, the most reliable way of removing black mold from a water bottle is simple, vigorous, mechanical cleaning with a soapy bottle brush. (Use a soapy pipe cleaner for intricate water bottle caps.)
Optionally, soak the bottle in warm, soapy water beforehand.
Never boil double walled containers. The expanding air inside the walls can also cause the bottle to explode.
Avoid boiling liquids around most plastic components, which may deform. Certain synthetic bottle components, such as pure steel, single walled cannisters, may be advertised as safe to boil.
Optionally, rinse with baking soda to purify fragrance.
Thoroughly rinse out soap. Position upside down in a drying rack.
Repeat the cleaning process as often as needed.
You needn't bother with rubbing alcohol, epsom salt, vinegar, rice, bleach, boiling, etc.
Like spores of bread mold in a bakery, black mold may very well arrive on the surface of factory fresh water bottles. In theory, you could fashion a pristinely clean robot to assemble a rather sterile water bottle out in the asteroid belt from raw, inorganic materials. But as soon as the bottle arrives to you on Earth, a black mold spore floating in the air is likely to randomly land on it. For better or worse, black mold is here to stay.
Black mold will grow most anywhere that is regularly wet. There is no permanent cure for mold. Instead, the approach is to regularly wash off mold as soon as it is seen, and to take practical steps to reduce how quickly the mold grows back over time.
Water bottles with wide mouths, and ideally clear sides, are easiest to inspect for mold. If you've been using an opaque water bottle for any length of time, then it likely harbors black mold spores that are difficult to see. You won't even know that you're drinking moldy water.
Water bottle caps often harbor mold. The more intricate the cap, the harder it is to clean. Prefer simple caps, preferably advertised as safe to boil, with only large, and few, nooks and crannies that a soapy pipe cleaner or finger can reach.
Avoid pouring beverages with sugary or oily ingredients into the bottle. Use water bottles primarily for water.
You can pour in commercial sugarless beverages, or make your own by adding some fresh fruit chunks or concentrated fruit juice. Citrus discourages microbial growth.
The alcohol in sugarless cocktails discourages microbial growth.
Ice also discourages microbial growth. Though avoid freezing a filled water bottle, as expanding ice can cause the bottle to explode.
Regularly rinse out the water bottle between refills.