For hot parts of summer, you definitely want to have more watering options available, even if all the birds are fine with nipples. Way too easy for them to get dehydrated or heat stressed when talking about high temperatures like that.
Ice chunks and regular EL doses during heat waves here.
I give EL in extreme cold too.
If they aren't drinking they won't eat.
I
love HN's, been using them for 6 years.
Especially in the winter.
Can put them in all sizes of buckets, jars, bottles.
Bottles work great in a rate when isolation is needed.
But it does take time and observation.
I've had all age birds either pick it right up within an hour...
....and others that take
weeks to
really figure it out.
Here's my thoughts on 'nipple training'.
First, it's good to know how much water your flock consumes 'normally', I top off water every morning and have marks on the waterers so I know about how much they drink.
Found they drank just as much from the nipples as they did from the open waterer.
-Do not train to nipples during extreme temps when dehydration is more of a risk.
-
Show them how with your finger(tho that might just train them to
wait for your finger),
and/or manually grab them and push their head/beak onto the trigger(easier with chicks than adults).
-
No other water source, best to 'train' during mild weather when dehydration is less of an immediate health risk. I do provide an open waterer late in day to make sure they don't go to roost dehydrated, especially young chicks.
It can take days or weeks to get them fully switched over, just takes observation, consistency, and patience.