So it seems the water from the pool can be given to the plant to make it grow, and by getting one kid caught by Ed you get a few minutes to raid his room. That helped me progress a bit, and I even managed to get the meteor arrested, and have access to the lab!
However, I can’t find an envelope (which I think I need to send this demo tape off), and I can’t get into the safe, so I’m stuck again. Bah!