I have been told that I should not use the water from my water butt for seedlings, why is this?
A rainwater butt often contains spores of the fungal disease that causes damping off.
This disease can decimate whole trays of seedlings at a time, causing seedlings to keel over at soil level.
Destroy infected plants and water the remainder with a fungicide.
Sowing thinly and evenly on fresh compost placed in clean trays or pots, watered from below with tap water can also reduce the risk of damping off.