The chickens will learn to use the nipples quickly. Here's an earlier post I did:
I think the best bet is to take their water away when you put them to bed and then encourage them to explore the nipples with no other water available in the morning -- take away their normal water long enough for them to be thirsty. Throw enough scratch or whatever to get them over by the nipples or call them if that will do it. Sit and tap the nipples so the water drips out. Usually they seem to be curious enough to investigate that sooner or later one will take a peck at it and then realize "OH MY GOD THERE'S WATER IN THAT THING!!!" Then the others see the first one drinking and it's the usual "'WHAT DID YOU FIND --I WANT IT!!!" At least that was my experience. I did see a couple people say they put a little peanut butter on the tip of the nipple to get them interested.........Depending on your set-up I would think about 8 nipples would be right for 25 chickens. As you saw I liked setting up an indoor tank to avoid having to carry water outside. If you set up something like that ask for PVC that is safe for drinking water. If a hose is involved use one made for an ice maker or for RV drinking water NOT a normal garden hose which is likely toxic. Other posts.......
We don't keep water in the coop at night unless it's really hot. The birds are out all day running around the yard until they are ready to sleep and they drink from a chicken nipple waterer fed from the house. If temps are going to be below freezing overnight we add some hot water to the tank and run it out the pipe before bed. If it's going into the 20s we throw a blanket over it. This seems to be working fine. The chickens go for water in the morning but they rarely seem to be anxious about getting there. In the summer we can easily add ice to the tank. Adding some collodial silver and covering the tank so that it doesn't get light work well to prevent algae growth....................................................
Yes I've read of people having problems with nipples from
Ebay, China etc. Following are the ones I got and have had no problem
http://www.qcsupply.com/farm-livestock/waterers/nipple-waterers/420006-poly-threaded-body-nipple.html
The Farmtek ones seem good but the shipping cost is high. I used an 11/32" bit and it was a tight fit into the PVC pipe. I put the nipple in my portable drill to help it get started. It might (?) have helped if I wet the threads. I used plumbers tape....BTW you cannot use normal hose pressure with nipples..........if you want to go the pre-made bucket route these are BPA free
http://cheerychicks.com/store/index.php?main_page=index&cPath=5 ...............................re

ight of nipples: from what I've read the nipples should be at a height where the bird has to reach up a little to drink -- this way the water goes down their throat. And they should be set at the height for your TALLEST chicken. Then put pavers, bricks, wood under some of the nipples to make the height right for the smaller birds. For this system the nipples are 19" off the ground for the leghorns and the we put two pavers for the smaller ISAs. Both use both anyway...............nipples are the standard method in the poultry industry -- no industry would use a method that would decrease production when other methods were easily available. Our birds not only drink from them -- they shower! By which I mean they take a mouthful and preen themselves with it -- you can see their feathers getting wet
FarmTek bucket video :
https://www.youtube.com/watch?v=hfv_A00rTgk