Thanks to all for the good info and references. We have been considering putting in a cistern here, some 9 years of drought in AZ, but needed more info on specifics. This has been very enlightening.

In the Midwest, dry underground cisterns kill people every few years or so. I think that the CO2 (or some other gas) collects in them, and people climb down into them and pass out and asphyxiate. Just keep that in mind if ever going into one.

That is almost the start of a thread about confined spaces and confined space entry. It might be a good thread to start if it does not already exist.

I'm sure you're right, it's nothing magical or special about cisterns. Where I'm from (South Dakota) there are a lot of old ones, and people forget, climb down them, and die. Then their family members panic, rush down, and die with them. Then the firemen with oxygen get the bodies out, and it's a big news story for a week. Then a few years later, people forget, and the cycle starts over.

I watched a news story about 3 volunteer firemen who followed each other into a liquid manure tank once.
The farmer had stuck his head into the inspection hatch, got hit by the H2S gas and fell in. (not sure what he was trying to do there, something about the pump I think.)

His son tried to reach in and drag him out, 2 down.
The second son called the fire department and they did the same thing as son number one, one after the other.
One tank, 5 dead.

Most people just don't understand the hazard of confined spaces and if they see somebody go down their first instinct is to reach them and try to help them.

Ed, there is a guy down near St David, I think, that is considered one of the experts of reclamation and grey water, I don't recall his name or business, I'll try to find out for you.

Oh, I forgot to mention, we had 2 cisterns, front and back, at the old Ohio Homestead, with big concrete covers, scared the dickens out of us as kids, that's where the monsters lived.

So I agree, they are dangerous!

Seriously though, they had been long unused, but we left them intact just in case. With the covers secured, they seemed okay.

thanks for this info. I was just checking out a 600 gallon cistern for about $900, but it was above ground.

It seems that the main appeal to an underground cistern is an improved ability to catch runoff and stay dark (anti-algae). Being underground doesn't give you the land back because you don't want to be doing anything on top of it (for safety's sake)

The above ground cistern has the appeal that you can't fall in it (ok, "as easily") and you can drain it from the bottom... the whole gravity feed, head pressure situation. And rainwater is generally safe to use (although rainwater running off your coal tar roof would not be).

Still, I'm not sure if the above or below is clearly better.

Is there any other benefit I'm missing?

Some thoughts

Pros above ground
1. gravity drained, no need for pump and power for pump
2. easier installation

Cons above ground
1. takes up space
2. may be seen as an eyesore
3. more susceptible to damage (UV, vandals, lawn mower, kids, etc)

-Blast

Additional, possibly paranoid, above ground con:

4. shows that you have a water supply