Ben Tolhurst

Chloramines are more stable, and thus don't leave the water as quickly, but they don't use those in my area, so it's not an issue.

Chlorine is unstable and not very soluble. It won't stay in water for long unless it's under pressure. Even fresh out of the tap the chlorine content is not nearly enough to actually kill anything, not even bacteria, much less far more resilient fungi (at least not in British tap water. I guess things might be different where you live), and if you leave the water to sit for a little while it will dissipate completely.
I would be far more concerned about rain water killing the mycelium, to be honest, as that stuff is likely to gather all kinds of bacteria and fungal spores in the collection process, so you'd need to very thoroughly sterilize it before you could use it.

Just an update: I have since removed the still living spawn from the coffee and have for now put it on just damp cardboard to try and spread it a bit. Once it has colonised that, I shall try growing it on a 50:50 cardboard:coffee grounds mix, which I read is a lot easer than pure coffee grounds.
The birdseed one is actually growing far better then I had thought, although it was drying out a bit. So I've added a bit of water to it but otherwise I shall leave that one be for now.

I'm trying (for the first time) to grow oyster mushrooms at home, on a fairly small scale.
I have, however, run into trouble. The batch I have growing in coffee grounds seems to be doing nothing at all, after a week (I even shook the bag to find the spawn, and the mycelia have grown not 1 mm.). I know the temperature it right, and I'm fairly certain that my pasteurisation and general cleanliness was adequate (there aren't any moulds or anything), so can anyone suggest what the problem might be?
My other batch is in some old birdseed (mostly millet, which is apparently good for growing oyster mushrooms), but despite previously heating it, the birdseed is now germinating. I assume this will be detrimental to the fungus' growth, since it doesn't grow on living things? That one seemed to be doing rather well, too, until the birdseed started growing. Would you recommend I remove the growing mycelia, such as they are, from the bag and put them in a new, definitely not alive substrate?

And I know poor quality spawn is not the issue, because I put some in a jam jar with some damp cardboard (to cultivate more spawn for later, in case of failure), and that's growing like mad.