[kaolinite]

Oh right, I've not actually tried altering the water - I really should give it a go sometime. I just use tap water - the water in my area is ok. That's another one of those things that may make a bit of a difference, but nowhere near the difference that getting good coffee and measuring properly will make. Of course, if you're already doing both of those then there's no reason to give it a go. Thanks for the idea.