I need some advice.
I have 2 large black walnut trees that do a beautiful job of shading my house while still providing enough light penetration to let me grow some things under them. As soon as I moved in I acquired 2 large rain barrels, and built a small swale through the middle of the yard with the intent of feeding the excess rainwater into it. Once everything leafed out however, I realized that juglones from the leaves and catkins were leaching into my rainbarrels and contaminating the water.
If I feed this water into the swale it will contaminate the ground all the way through my yard, not just under the walnuts! I have read that most of the juglones run down the bark of the tree during a rain, and drip off the leaves. Does anyone know if a first flush system might get rid of a large portion of them and then I could more safely collect the water after that?

I don't have direct experience with this problem but...

It seems like the rain dripping off the trees would happen after the first flush was full.  If it were my issue to mitigate, I would probably just plant species resistant to juglone.  The following list has some inconsistencies (elderberry is on both the susceptible and resistant list, as are a couple others), but there's plenty there to chose from.

http://web1.msue.msu.edu/msue/iac/greentip/blackwal.htm

You might be right Osker, I should just suck it up and stick to the juglone tolerant list, and await my plot in the community garden so I can grow non-tolerant crops there.

I have found a lot of inconsistencies in the research I have done as well. Some, like your list, say that tomatoes and peppers don't like walnuts and I have seen elsewhere that they do. Mine seem to be thriving under them, and are definitely outperforming the ones out in the sunny middle of the garden where they should not have too much exposure to juglones... I guess a lot of it is experimentation.

Thanks for the new resource.

interesting..wonder if you could place your gathering system on the opposite side of the house to avoid that problem?

It's a pretty small house so the leaves end up getting into all the gutters. There would be less direct dripping on the other side of the house, but still lots of tree fall.

You could just run that water back under the walnuts and plant juglone-resistant stuff there.

You could clean your gutters frequently so there won't be a problem.

yeah myself i think i would probablly screen the gutters and maybe put in some pipe or or something to keep the water free of the Juglone until it is away from the walnut trees..so it doesn't kill off the rest of your plants

as for barrier trees and plants you can do that for the runoff too..see Gaia's garden..for info on barrier plants..also I think some other books had some good info but can't remember which.

if you search for walnuts or juglone on this site there might be some info that will help you