There are a number of ways to carry more water bottles. Most bikes have water bottle mounts on the inside of the diamond frame. So that makes 2. Touring bikes have another place for a bottle on the outside of the diamond triangle behind the front wheel. But that would mean having someone stick the mounts on your bike which could damage the frame.

I have seen triathaletes with 2 bottles mounted behind their seats. With the 2 on your frame and 2 on behind your seat, you would have 4 which should be plenty.

Of course, you could go an alternate route and get a camalback.