Monnie, it is ok to introduce at any time but usually for bfed babies it isn't necessary. Personally I did introduce it after 6 months or so, as I like to know that they would drink water if necessary. And certainly on those hot days it won't hurt. It is recommended that you use cooled boiled water until about 12 months, and I did this for Jack. But Tom was on tap water earlier as he would just drink Jack's drink anyway so I couldn't stop him. No harm was done!!