Run-off water collection

The 35 year saga of the Los Osos sewer nightmare is coming to an end and we are due to connect between June and December. I used to be excited about this because it would give me more land for trees, but with water restrictions so draconian I really couldn’t support any more trees and can just barely keep alive those I have. Now I just want it over with.

We’ve been given a couple of options for the decommissioning of our septic tank. One of those involves sanitizing it and using it as a cistern. I already have a 550 gal tank in the back yard that is connected to one downspout and might add another this Fall. The septic tank (in the front yard) is about 1000 gal. Obviously a useful resource.

Here’s the issue: there is a downspout on the side of the house that could be plumbed to the septic tank with considerable effort. That downspout services only a small amount of roof. Across our huge driveway (think: 2 cars + RV size) is another downspout that services much of the roof and drains into the low point of the driveway. From there it flows to a drain adjacent to the septic tank and thence by a long pipe, under some sidewalk, under a gate, to some sidewalk along the side of the house and eventually the yard (specifically apricot, cherry and plum trees in its path). But that water also includes run-off from our concrete/asphalt driveway AND whatever makes its way down from the street (the drain is 5 ft below street level and there are no curbs or driveway aprons).

So…in a way we are already using this street/driveway/downspout water on at least a few of the fruit trees, simply because that’s how the drainage was done long before we got here…but should we be?

I’ve read that you shouldn’t even use roof runoff if you have asphalt-based shingles. Street runoff is spoken of in terms even more dire.

Our driveway (concrete and asphalt) is “clean”. We don’t park on it and there are no oil deposits. I can’t speak for the street, but it’s a side street which gets its share of suburban traffic. Our “soil” is very fine dune sand, hydrophobic when dry, but once wet, like a sieve.

I’m stuck in this dilemma. Anyone want to offer an opinion?

My opinion is personal, probably the best idea would be to have a “runoff” water sample tested. We use rain barrels that are fed from our asphalt shingle roof. I really wanted to do a metal roof but it was cost prohibitive for us. After reading about all the other things in our tap water (contraceptives, antibiotics, antidepressants, etc) I rationalized that after filtering through soil, I was comfortable with any risks of uptake into fruit trees. I don’t use that water in veggie beds or anything it would contact edibles directly. Good luck with your conversion!

If it were possible, a cistern could sure store rain runoff from the roof for irrigation or other purposes. A mere rain barrel is too small for big things.