Check to see if the bike course has water points. For both of my 1/2IMs this summer I only had two bottles but picked up water/sports drink at the hand off points.

I am training for a Half Ironman but haven't done one yet so I am far from an expert but based on my training rides and the advice of others, my plan is to carry two bottles and then refull during the race plus I will have room for one handup bottle during the race (I have 3 bottle cages).

I would say that most if not all HIM races would have water stops. I just did Ironman Cancun 70.3, which was SUPER hot and we had 7 water stops. It helped that the course had a 3 loop part but still. I had 1 water bottle and one aero-bar water bottle. The aero-bar water bottle had gatorade and my water bottle was water. I would get the gatorade and just dump it in my aero-bar water bottle and just exchange my water bottle. One thing to know/remember is bring an old water bottle or 2 for the cage, since you just exchange bottles you don't get yours filled up.

Good luck,
-triNick

The 1/2 that I have coming up this weekend has water bottle excanges at 15, 30, and 45. So I will be bringing one water bottle and couple flasks of perpetumn.

I had 2 rear mounted water bottles filled with Gatorade endurance. It worked fine for me but it was 60 and drizzling most of the day.

My strategy is to carry one concentrated (insulated) bottle of Hammer Sustained Energy on the seat tube. I mix my Endurolytes into the concentrate. I carry 2 hours worth. After 2 hours I switch to gels. I keep a couple gels in a bento box.

Then I use a profile bottle on my aerobars. This I fill with water at the start and refill with water throughout the race at aid stations. If it's too long between water stations I'll put an extra bottle from an aid station in the bottle cage behind my seat.