Regarding a well, if you have sandy soil and a high water table, you don't even need to have a well dug.  Just buy a 2" well point (aka "sand point') and the necessary steel pipe, and this can be driven directly into the ground. Google [driven water well point] for more info if interested.

Here is a link also:  Driven Point Wells pdf

Interesting, but risky; Florida has just recovered from an extended doubt and the water table has risen quite a bit. I would be afraid if we did a Driven Point Well and experienced another drought we would literally be left high and dry.

David
Perhaps I can of help for your situation.  
I represent Sun-Mar Compost toilet systems and by installing a compost toilet you not only solve your problem of drainfield septic tank but also add to preserving the environment.
Unless you feel there is an upcoming major drought I am not sure why you would need such a great quantity of water, normally 500 gallons is sufficient.
The monolithic concrete dome I built in Inverness has a gray water system with compost toilet.
Gray water will water the lawn the compost will fertilize the plants.
www.safedomes.com

Thanks,
DaveS 

Dunno why you couldn't bury a rainwater tank, high water table or no. It's not like the tank would contaminate anything, or that seepage into tank would be a problem either. As Brock says, it could pop out of the ground, but that never happened to me in Texas over a 20 year period. The only lessons I learned is: a: when it rains in Tx it pours, thus limiting its utility; and b, fill the thing the minute you drop it in the hole if you don't want to find it floating after an overnight storm (see 'a' above.)
Your soil will be different, of course. I'd ask your septic contractor if it can be done. Chances are he'll be burying storage and dose tanks for your sand mound.
BTW, I used gray water in this house by plumbing it separately and using two tanks in series so that the gray water tank, if it wasn't pumped in a timely manner, overflowed into the black water tank and thus into the drainfield. My lawn was fragrant for an hour or two after sprinkling, but it was very, very green. Dunno what the state would say about it today, but some states bless drip irrigation after filtration: http://www.premiertech.com/ecoflo/en/
In yet another approach, these folks claim to cut water use by 30 to 40 percent by plumbing gray water separately, as I did, treating it and using it a second time to flush commodes. http://www.bracsystems.com/home.html
I'm splitting the waste system in my new house even though I don't expect water problems. It's no biggie until you add drywall.

When you say the septic will be above ground, you realize that a typical sand mound installation has at least one and possibly two buried tanks, right? Those tanks will be larger than normal if the mound requires regulated doses. Mound systems cost twice as much as conventional septic systems. Alternatives like Ecoflo cost more yet, but are worth exploring in challenging conditions because they work better, assuming adequate maintenance.
A cistern, it seems to me, is riskier than a well for what you want to do. If it doesn't rain, an 8,000 gallon tank is empty in three or four weeks. (100 gallons/person/day plus 1,000 gallons/month for the pool.) A long drought would result in brief interludes of very expensive, site-treated drinking water, and far less benefit to the environment than the same money spent on reducing water use.
There is no substitute for consulting local people who understand your climate, soil and laws.

DaveS

No offense intended. Just trying to give you the benefit of my 20 years of living with a cistern, the upshot of which is that nothing opens the heavens more reliably than a full tank. The advantage of a composting toilet is that you don't need celestial cooperation. My point about a well is simply that you should trust a cistern less.
You're right to do your own research because builders don't stray far from what they've always done. Even if your build team is top notch, you want to approach this like a nuclear arms treaty: trust but verify. On the last point, are you sure your builder didn't say $4k extra for a sand mound? I'd pay $14k for a pumped mound system in Pa and perhaps $16k for an Ecoflo. I doubt that $4k would get me the materials.

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