We had 2.5mm for the second time this week.
I remember in the first of the How to Be a Gardener programmes, Mr T showed that an inch of water goes down 6 inches, so we'd need a good couple of inches here to make any appreciable difference to the soil conditions. More, perhaps, since I don't think the experiment assumed bone-dry dust to begin with...
I am not watering the established plants though this year - I'm trying to teach them to fend for themselves, in case we get a drought order and can't water at all. Still watering the seedlings though.
moonbells