Most new bottles will not develop a moldy look, but old bottles can. Not that it makes a lot of difference! There is no way to get rid of the mold growing inside the bottle because water has absorbed it and it will cling onto anything else in contact with it which means even more germs icky beyond what you thought! But if you do replace your water bottle every so often than the mold will be less likely to grow.
So basically, when purchasing a new water bottle there’s no worry about containers getting molded up, enjoy your hydration! When recycling they might become difficult but if we just keep them out of our mouths and don’t let our mouth hit dirt then we’ll be okay.