A couple of interesting sources, also follow links in page:

http://www.irc.nl/page/29189#information

http://dfwnetmall.com/energy/rainwater-catchment/first-flush-diverter.htm

Suggests a first-flush setup may do little good:
http://www.harvesth2o.com/first_flush.shtml

A complicated version:
http://www.slowsandfilter.org/first_flush_diverter.html

http://www.harvesth2o.com/RainwaterHarvestingManual_3rdedition.pdf

A thesis exploring various forms of first-flush. evidently the agree upon terminology, devices. An interesting read but a bit tedious:
http://rainwaterharvesting.tamu.edu/Justin%20Mechell%20Thesis.pdf

Reading/scanning most of that I'm struck by how little hard information there is that is applicable to any system any average homeowner is likely to build. Also how much overlap there is in sources, and how much deciding on a system is going to be pretty much like it was twenty years ago when it was handymen and backyard tinkers assembling systems based on their own intuition and estimations.

Yes there are some guidelines and lots of good ideas and things to think about.

I suspect that the safest course would be to use collected water for drinking only after it is chemically treated. I might give it some basic testing. Or simply make coffee or tea out of it so there would be far less chance of microbes being an issue.

Hilarious! But I guess you don't really need to direct the overflow away from the foundation like we do here in the North. We have basements, and one of the main reasons to have gutters is to direct the rainwater away from the house, so it won't flow into the basement. You probably don't have a basement, so it's not a big deal.

Thank you both for the links, I'll have to go through them.

One thing I have noticed about discussions on rainwater harvesting is that people are worried (possibly excessively) about contamination, automatically comparing it to what they think comes from their tap. They don't seem to realize that most municipal water supplies aren't providing pure water. Even chlorinated tap water isn't perfect, it simply reduces pathogens and contaminants to what is considered a safe level.

For instance, here are the test results for Los Angeles (2010)

It shows that there are still fecal coliform bacteria in the water. It shows that there is still Acrylamide, Epichlorohydrin, Aluminum, Arsenic, Barium, Nitrates, Radionuclides (like uranium), plus the stuff they add to disinfect the water: Trihalomethanes, Haloacetic Acids, Chlorine, Bromate.

The bottom line with rainwater harvesting is that it can be the difference between having water and not having water. If you store water, great. With rainwater harvesting you can bathe and wash clothes. If the disaster is extensive and you run out of your stored water, you've still got options.

Sue

Be sure and keep the setup hidden behind a fence. In some (many?) municipalities, you do NOT own the water rights on your property. Even to collect rainwater. I've never heard of that being enforced around here, but I know it's the law in my area.

Susan - of those links you might want to go over this one first. It is a guide from Texas and it pretty well covers all the basics and, IMHO, would serve as both introduction and overview.

http://www.harvesth2o.com/RainwaterHarvestingManual_3rdedition.pdf

GoatRider: Only a crawlspace, and even that's up towards the front of the house. Back by the tank it's just a concrete slab. I know what you mean about the basement issue, though. In the springtime, I could fish in my old basement back in Iowa.

Thanks Art! All good information. Provides a great deal of food for thought.

It does look like there is some guess work still involved in determining first-flush volume. In this case it would be the old axiom, "Better safe than sorry". Especially if you are going to consume it rather than use the water as "gray" water.

Nice looking setup sotto ... and I have a general question about this. I am looking into catching the rainwater from my own gutters for use as gray water. Is there any advantage of a system like sotto has over just an ordinary rain barrel?

addition of one of the Sawyer .1 micron filters would strain out the critters, but not virus or anything dissolved in solution, but not much does.. possibly clear glass aquarium type container or coil of clear tubing to get some UV help... might try a final activated charcoal can (aquarium supply house)for halogens....

first volume dump
biomass slow sand
UV exposure
Sawyer
charcoal

might have something...

Following this thread reminds me that in the 1930s the Coast Guard constructed the Mother of All Water Reclamation Systems, which included a flat sloping concrete apron, roughly fifty yards by twenty yards. This collected the winter rains for the use of the newly erected lighthouse and quarters on Anacapa Island.

Unfortunately, it also collected the physical residue deposited by the thriving flock of sea gulls which inhabited and bred on the island, making the water distinctly gray. Eventually the system was abandoned and potable water was (and is) shipped to the island and stored in conventional tanks.

Today the catchment basin makes a really fine helicopter landing pad.