I switch at about 4 weeks old - and put it up on bricks or something else to elevate it.
It really does help to keep the water cleaner. Also, they're fully feathered by then and big enough that falling in and getting chilled is no longer an issue.
I have mine hanging from a hook in the coop to keep off ground..and I put mine on big ones soon as they hit the coop. had to have little lower at first but as they get bigger I keep raising it up some to about height of top of there backs..
Mine are still drinking out of chick waterers, and they are 9 months old! Which is fine until it gets warmer and they will start drinking enough water that it will become a pain to refill all the time.
IMO, i just change waterers when they seem to be using them too fast for me to keep them filled daily. At present i use one of those dog waterers,(the kind that come with a three gallon tank) for my big girls and guys. and when my new ones start having to be refilled more than once a day then I use the gallon waterer.