Each individual perspires different amounts in different conditions. For me, I need to drink between 12 & 16 ounces of water every hour in moderate heat. When it gets above 90 degrees, I need to drink 20 to 24 ounces per hour. While cool drinks have appeal in hot weather, your body absorbs water quicker when it is closer to your own body temp. Hence, I never ride with ice in my water bottles.