Your issue is a leak in your map, but that's totally independent from the trigger_hurt volume within the water. Compile the map, then open the compile log (the file is saved in the same location as your vmf and bsp file), then go towards the top of the file. Look for anything that says leak. It's usually spelled out in capital letters because it's a compiler breaker. If you load your pointfile (the file that the compiler makes when it encounters a leak) you'll see a red line that points to the entity that leaks and where it's leaking to. Seal the skybox in that location and you should be golden. That is, if nothing else is leaking. If that's the case repeat the process until a search window pops up when loading a pointfile. If that's the case you have no more leaks.