Mine had boiled water in summer, though they were not breast-fed.
It is hard on a breastfeeding mother in summer to keep quenching the baby's thirst as well as his hunger - and it must make her need a lot more water too, to be drinking for two.
Mine were bottlefed, and when I was trying to get them off a feed in the middle of the night, I would tank them up last thing, then give them boiled water if they woke. Very often they would fall asleep after a short drink. I believed that they were thirsty, not hungry. After a couple of weeks of this, they did not bother waking up at all - not worth it for a measly drink of water.