A refillable bottle holding water is a warm damp container with a lid, and that deserves more thought than it usually gets.
Why Water Is Not Sterile
Tap water is safe to drink and it is not sterile. It contains organisms in small numbers that are harmless when the water is fresh.
Left standing at room temperature for weeks, particularly with any organic material in it, those numbers rise.
Add a leave-in conditioner, a plant feed or anything with sugars or proteins, and you have supplied nutrients as well.
The Signs
- Cloudiness in a previously clear liquid
- A musty, sour or unfamiliar smell
- Slime or a film on the inside of the bottle
- Visible specks or floating material
- A biofilm around the neck and inside the cap
Manufacturers advising warm water and hand washing rather than a dishwasher, of the kind noted at https://flairosol.us.com/, are pointing at the practical routine: regular gentle cleaning rather than occasional harsh cleaning.
Where It Actually Grows
Not usually in the open bottle, which is easy to see and easy to wash.
In the dip tube, the trigger mechanism and the threads, where a film forms and nothing reaches it. That is the part people never clean and it is the part that matters.
Flushing warm soapy water through the mechanism, then clean water, is what deals with it.
Why It Matters Where It Is Sprayed
A mister used on a face, on hair or on food surfaces is atomising whatever is in the bottle and putting it in the air you breathe.
That is a good reason to keep water bottles fresh rather than topping them up for months.
The same applies to anything sprayed near a person with asthma or a respiratory condition.
The Working Routine
Fill small quantities. Empty rather than topping up. Flush the mechanism weekly with warm soapy water and rinse it through.
Dry with the head off where possible.
Distilled Water Helps
Particularly in hard water areas, where minerals also block nozzles.
Do Not Store Mixes Long
Days rather than months.
Label Everything
Clear liquid in a clear bottle is unidentifiable.
Replace Rather Than Rescue
A bottle with established biofilm inside a mechanism you cannot reach is worth replacing.
Dry With the Head Off
So the inside of the mechanism can actually air.