this is less a problem with the bottle and more a problem with how you're not cleaning them well enough.

The only thing that ever comes in contact with my water bottle is water. It is always spotless.

You are contaminating it with your mouth when you drink from it. If you put sugary stuff in there, you are basically carrying a petri around with you and asking why its growing stuff.

you can clean them daily, they get black spots

Daily?! I clean mine weekly and I put coffee and milk in them. I drink my coffee by lunch and rinse them out 3x. I turn them upside down and air dry the 2nd half of the day. They're dried by end of day. Do that 5x a week. Wash on the weekends.

Just learn how to clean them and clean them. There is no magic bottle that doesn't.

You're probably going to have the easiest time just cleaning them periodically.

If you want to have something that's intrinsically antifungal, instead of stainless steel, you could get a copper-alloy water bottle, like bronze or brass.

https://en.wikipedia.org/wiki/Antimicrobial_copper-alloy_touch_surfaces

Antimicrobial copper-alloy touch surfaces can prevent frequently touched surfaces from serving as reservoirs for the spread of pathogenic microbes. This is especially true in healthcare facilities, where harmful viruses, bacteria, and fungi colonize and persist on doorknobs, push plates, handrails, tray tables, tap (faucet) handles, IV poles, HVAC systems, and other equipment.[1] These microbes can sometimes survive on surfaces for more than 30 days.

I wouldn't bet on it stopping growth on the gasket, though.

It looks like this claims to be copper (which if correct, I would think would be really prone to denting):

https://www.amazon.com/Adonai-Hardware-Hammered-Copper-Bottle/dp/B09MZ9VYJS

This vacuum flask says that it has a copper internal lining:

https://www.amazon.com/OUTSIDER-Stainless-Vacuum-Insulated-Bottle-Thermos/dp/B0BX7C1MDK

I use a stainless steel insulated bottle and I clean it with Polydent tablets, like for cleaning dentures. It works incredibly well.

32oz wide mouth Nalgene for me. I have 3 and cycle them every 2 days. Dishwasher when I run it and bottle brush once a week. Never a hint of anything.

stainless steel or glass. Those are your options for growth-free stuff. Even then, water only, or you're only creating a science experiment. Even then, wash frequently or you're only creating a science experiment.

Reading other replies, I find it interesting. I use a manna water bottle (big 128fl oz one) and typically drink about half a day. I normally can let it be for quite awhile (a few weeks I’d say) before feeling like I should clean it.

I'm a huge fan of glass bottles because of their ease of cleaning and resilience to getting funky. The lid is the only place you have to be careful of, but that's usually a lot easier to be mindful of

FWIW water grows less mould than water with sugar/flavor/etc.

Assuming USA, kleen kanteen, with a simple screw-off cap. Or yeti with those slider caps. Personally as a desk worker my water jug has no cap.

For cleaning, soaking for 20 min or so with hot water and something like unscented oxyclean, powder brewery wash, or a bit of dishwasher powder works very well at removing organic matter - for stainless and glass.

Youtuber "Miranda Goes Outside" just came out with a bottle that's supposed to resemble a Smart Water bottle in form-factor but have the entire top unscrew ( in addition to the narrow standard bottle cap) for easy cleaning.

I have a stainless steel Nalgene bottle that I only use for water. It does have a plastic cap that is a bit unsatisfying. But, I haven't noticed any mould issues and it's perfectly ok to clean the metal part with boiling water or with bleach.

I have a Bubba water "bottle" I've been using daily since 2019. No mold, no issues. https://www.amazon.com/dp/B079B962YQ Non-affiliate link.

Mold = dust/residues + dampness. Clean your bottles, and keep them dry when out of use - you can keep water filled bottles pretty long in the fridge.

My 4 year old bottles stay filled in the fridge; when a bottle travels with me, coming home i wash them with my bottle brush and a small amount of dish soap and either fill them right back up and put them in the fridge again, or i keep the cap off and let them dry thoroughly putting them upside down so droplets can get out. Anything else is just an invitation for mold.

Never had mold in my Camelbak chute

Invest in a bottle brush and clean your container well.

I really like my owala water bottle. I don't think there's any hidey-mouldy places, and it's water-tight. I also appreciate the dual straw&chug mouthpiece. Pretty clever imo.

I would just not care about the biofilm and wash it regularly. If you fill the bottle from a clean source and it doesnt smell or taste strange, the water should be fine for consumption.

You know your fresh water pipes also have biofilms in them? If it isnt contaminated, the microorganisms there are harmless. So if you get clean water from the pipes and your mouth has a healthy microbiome, where should potentially harmful microorganisms come from?

Only in rare amounts from the environment when you open the bottle. For that to create a buildup will take time. If you properly wash your bottle like once a week you should be fine.

No bottle will stay clean if you dont wash it from time to time.

I wish I knew. Scouring a metal bottle by using a bottle brush with a little water and rock salt or baking soda can help de-scum the films that lead to mold.

Historically, these are the consensus fave in reusable bottles:

https://en.wikipedia.org/wiki/Calabash

I like wide mouth bottles that match the diameter of the rest of the bottle, because they are the easiest to clean. You can even just toss them in the dishwasher depending in the material.

I also try to only buy titanium bottles since they last a lot longer than stainless steel. Some brands are too expensive but ive gotten lucky in the past with no name brands.