I would go in and flick it a few times a day and they would run up and check it out. I would keep doing it until one was interested enough to start pecking it and get the water. Once one drinks from it they all will. It's all I use for my chicks!
I just made one this week. I was worried about the same thing. I flicked it a couple of times and my nosiest baby came over to check it out. Since they are all such nosy copycats, they all copied her and all was well. I was able to take out their dirty waterer the same day.
My 12 new babies picked it up today in less than 5 minutes. I just moved the nipple around, making sure it was noisy, they ran up and immediately started drinking after the first couple figured it out. The only problem I am having is one of the nipples leaks. I'll contact the manufacturer tomorrow.