From my understanding, it's never been a lack of knowledge for them to drink from standing water. They will do it if they have to (typically drinking from drops on a leaf for instance). It's more of: They should really never need to drink from standing water. With a little supplementation here or there (during a dry season) being an exception.
The waterfall fountain machine is likely dangerous. If it is recycling water, you are putting your chameleon in harms way of bacteria that can make him really sick. Maybe you happen to have some waterfall system that does NOT recycle water. That may be an exception, if that is the case. But in general, if your chameleon IS drinking water that way, then they are likely not getting the proper hydration they should be getting at night, while they are sleeping.
Drinking from still water like that, it is likely a last resort for them as in the wild it would likely put them in danger to go down to the ground just to hydrate.
I don't know your setup, or anything like that so it's all speculative, based on what I've learned. But this is where I am. Maybe look into your numbers and setup and just make sure your chameleon is getting the proper hydration.