First, remove all other sources of water (and do this on a moderate day to lower risk of dehydration).Thanks for the response. How do I train them to use the nipples since they've been using the open method forever or do they just figure it out on their own?
If you have some tame birds, pick them up and use their beaks to press on the silver toggle, let them drink the water, repeat, and they should start figuring it out. If they're not tame enough to easily handle, then stand close to the waterer and when they're paying attention to you, "peck" at the toggle with your finger and hopefully a few curious birds will come investigate. You don't need to train each individual bird, if a few figure it out the others will follow.