This app was mentioned in 2 comments, with an average of 1.00 upvote
1) Refill as you ride. There are apps for you phone that help you find water fountains - WeTap for iPhone and TakeABreak for Android. This is my go-to option. I've been surprised how many water fountains there are in remote areas (100 feet from the road on a park trail, behind a firestation, etc.).
2) Carry more water. Bigger bottles or an extra cage. The Zefal Magnum 1L (33 oz) bottles are a good choice. As far as an extra cage goes, an SKS bottle cage adapter on the seatpost works well. An alternative is a Two Fish bottle cage adapter on the downtube.