This 1.7L pressure vessel was supposed to be part of the Hyperion II rocket. It was reinforced with fiberglass, and it failed at a low pressure of 6 bar. 

The probable cause of failure was that the epoxy resin did not cure well. A way to improve the reinforcement is by mixing the resin and the hardener better. Also, the epoxy is well beyond the shelf life and this could have also been a contributing factor to the failure.

Considering that I have very little spare time perhaps it is time to revisit the Robison coupling method of building water rockets.