above ground, underground, inside or outside? for drinking water or non-potable? How big? What is the source of water (rainwater harvesting, gray water or?)

Cheapest method is to dig a hole, line it with a membrane, fill it with gravel, and fold the membrane over top, then back fill. more capacity is available with manufactured structural grid panels instead of gravel (often used under parking lots). rigid cisterns are mo' money.

rain hog

The City of San Diego helpfully provides the following reference:

http://www.sandiego.gov/water/conservation/rainwater.shtml

I believe the county gives away kits.

When installing cistern, find a good place for it.  Aside from obvious issues of space and aesthetics, look for a spot where most of the water leaves your roof so you do not need to install too much piping to get the water to your cistern.

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Ah, thanks a bunch folks!  Excellent information.

Well it's a bit of a moving target, my client has a very high water assessment on the property, and I have been tasked with seeing if it would be viable to integrate a rain harvesting system w/ holding tanks for all the water needs of the house, completely standalone, no water from the city and no well. 

We are looking @ around 2,500 sf space, w/ two people.  Rainfall in the area is 15 inches per year, and I've got 9.5 acres to play with so space is not an issue.  Sloped lot, challenging but not impossible.

I've been penciling out what the typical consumption of water usage is per person, and the general size of the holding tanks.  The strategy would be to capture the water during the rain season to hold you through the summer.  The site is in Southern California.

Make sure the roof is tile, stone or metal!

wow. make sure your roof is as large as possible. small roofs can compound the collection problem, especially in dryer regions.

looked into dual chambered bladder cisterns? these seem to get a lot of volume and are fairly cost effective. worked on a project where we planned this, cost was under $3.5k for XR-3 PW.

if you are doing a crawlspace, the bladders can be suspended under them, which bypasses the whole, do we really have to dig a massive hole question.

9.5 acres is alot.  if the site is sloped a manmade wetland or a depression at the low end may be an interesting solution.  15 inches of rain? lets assume 12 inches to play it safe. There are 7.48 gallons of rainfall per squre foot.  (1 cubic foot = 7.48 gallons)  if you multiply 7.48 x 46,560 x 9.5 you get  3,308,553 gallons per year.    Thats 442319 cubic feet of water which can fill a 1 acre size pool to about 9 feet deep.  If the evaporation rate is about 5 feet per year (not sure, but in phoenix its about 7 feet per year so I would assume it is lower where you are)  you will get  about 1.4 million gallons per year.  To hold this above ground you would need a 1 acre wetland or pond that is 4 feet deep.  Now assume the average person uses 40 gallons per day and you have 2 people.  80x 365= 30,000 gallons per year.  That's alot of extra water for irrigation, so if you find out how much irrigation is needed you can use this math to size your pond.  Water can be pulled from the wet land or pond to an underground cistern that is lower than 4feet.  By doing this it will always be full and you won't need such a large cistern. water would move something like this (landscape-pond-filter-cistern-filter- house and irrigation pumps).  Not sure if you can get it to be potable, but the wetland should help with some remediation.  Good luck!

Also, if you collect from the roof only you will only get about 20,000 gallons per year which will not be enough to be 100% off grid, and thats assuming its a 1 story house and you collect it all.  You will also need a big cistern to hold enough for the dry season.

Thank you gentlemen.

If the project is going for off the grid don't forget to account for the electricity to run the pumps in the cistern!  Good luck.