Rescue systems are now available from both the air and the water.
Auto-Inflation Device: About Agama | Resetting the Agama
I put the Agama system to a realistic test (see the results here) and it passed with floating colors. Don’t bet your life on it any more than you would any other single mechanical device but it could easily save your bacon and gear if the unexpected water landing occurs.
Reserve (Rescue) Parachute
See more on Reserves, including repack video.
Fortunately I’ve never needed to use a reserve parachute but there have been times I was glad to have it and times I wish I did. More than other safety devices, a reserve adds an element of risk with the remote possibility of an accidental opening which could be catastrophic if it sets you down somewhere you don’t want to go. Historically that has proven rare and saves are more common than accidental deployments by about 5 to 1. But you must know what you’re doing, how to mount it and how to deploy it. A good instructor familiar with your model is best bet and the Powered Paragliding Bible also has good coverage of the topic. Here is information on choosing a reserve.