Need a quick answer please!

We will be leaving for the fair soon and it is warm out. Of course I keep her out of the sun, but is it ok to give her a small amount of water? I called the LC I use and she said yes 1/2 an oz is fine on a warm day. What do you think? She is 3.5 months

 I gave all of my kids a little water now and then around 3 months old.

I was told no water under 6 months old.  It throws off their electrolytes and sodium levels, and can lead to water intoxication.  Breast milk has all they need... even on those super hot days.  Babies are smart, and know when to drink for thirst or for hunger.  The foremilk is largely water, and is really all they need on hot days like that. 

L is 7 months, and has never had water yet.  We spend a lot of time in the heat, and I just offer him an extra bottle of breast milk.

 a 1/2 ounce at 3.5 months is unlikely to cause water intoxication, but I would still be very careful with water :)

I would have just stuck with nursing her as bm is all babies need to be hydrated. Hope you had a great time at the fair.