It all depends on the environment in which you're in. The radio datasheet says up to 100 meters line-of-sight. Of course, this is never the case in real life.
We've seen really busy locations with a bunch of radio interference and a bunch of people (i.e. columns of water) and seen significantly less range than this. You can mitigate some of this by switching to an alternative channel that is less used.
We're evaluating three areas of improvement in this area of range. One is to build in some additional channel-hopping for the network stack. Two is to evaluating antenna diversity and an RF front-end module that will amplify both the tx and rx for the radios--giving it not only longer range, but much better noise immunity. Lastly, we're evaluating an alternate radio altogether for longer-range, where we expect to get up to 1 mile between nodes in a dense urban environment, or up to 9 miles in a line-of-sight configuration.