Water bottles are advertised as being much more sanitary, and sure, they might not be able to poop, bathe, and get food in them, but you have to worry about sanitizing them properly. I wanted to get my guys a glass water bottle with stainless steel parts, but of course, not a single manufacturer produces products without any plastic (I'm paranoid about all those endocrine disrupters and other nasty chemicals leeching from plastic). Oh, right, I wanted to get them the water bottle for enrichment purposes.
Right, so I just give my guys fresh water twice a day after first washing their stainless steel dishes with soap (Ecover) and water. Their dishes are NEVER slimy because I wash them so often (I'm kind of surprised they aren't all germy). Also, I hang them in spots that they don't want to hang out (one's on the left wall of the aviary, away from their cage and their giant apple tree branch; the other is in the cage hung up high and away from their food to make sure that Rumi, my flightless girl, can still drink).
For Australian species (excluding lories and lorikeets), you can put a single drop of unadulterated (most manufacturers add harmful chemicals to their essential oils, so be careful!) eucalyptus oil in with fresh water in a stainless steel dish. I just started doing this a couple of weeks ago for their baths, putting a few drops in a stainless steel macaw dish along with fresh water, and my budgies and kākāriki love it! I use Now essential oil, and I checked out the company and whatnot before I began using it (I started diffusing the essential oil last year when Charlie was getting respiratory infections from his medication).
Also, to make things less gross, why not have a large bathing/food dunking bowl (thereby diluting the germs), and a couple of tiny water dishes up high? Oh, and stainless steel all the way. That stuff doesn't leech chemicals, is easily disinfected, keeps the water cool (unless it's freaking hot in their enclosure), and I find it doesn't get slimy if washed regularly.