If your Flume Bridge disconnects from WiFi, you will get an email letting you know.
You will also see a notification on your Dashboard as shown below:
To reconnect to WiFi, please click the "Fix here" link. You will then be guided through a series of pages that will help you reconnect your WiFi.
If your Bridge has disconnected it's likey your Water Sensor has also disconnected, once your Bridge is reconnected your sensor should reconnect on its own within an hour, if this does not happen please follow the steps in this article.