Water during breastfeeding: necessary or not

You have a baby, and there is a lot of joy in the house. But despite all the admiration and affection of a young mother for her child, she receives advice from everywhere. How to properly feed, how to put to sleep, how to dress and whether to give water. Often people of the older generation (grandmothers, usually) insist: especially in the heat, the child should be given water. Why do babies need it?