Pond where there is no natural water source

We would like to build a pond on our 30 acre homestead in SC. We have clay and rock and sand soil. We will fill it with well water, water catchement from the roof and possibly end our graywater filtration there. The best (clay) soil is pretty much at the higher elevation of our land. The lower elevations are mostly sand and we know that won't hold water.
One concern is keeping it filled without running our well all the time. One factor here in the hot dry south (although we have had bunches of rain this year) is transevaporation. Would it help to dig a deeper pond with a smaller radius. We are thinking about 1/4 acre probably. We are also concerned with keeping water in. With our sand and rocks that might be an issue. Any thoughts out there?
Wish Sepp Holzer lived down the street!

Good questions to be asking in advance. Some thoughts on your situation-

What are your objectives for the pond? Fish? Recreation? Beauty? Ecology? Figuring out your priorities is key to a successful project.
Finding an experienced and reputable local contractor will be the most important decision you make. A professional pond builder will refuse to build a project that is not going to meet your objectives. Ask around, get references, view some completed projects. Ponds are easy to dig and hard to fix.

You live in a relatively high rainfall environment so that is good. Is there any sort of watershed that will drain into the pond during times of high rainfall?
Using graywater would likely introduce overly high nutrient levels to the pond, even if it passes through plant filtration, so I would be a bit concerned there. Excess nutrients will make pond management a nightmare, with algae blooms and aquatic weeds. Have you tested your well water to know its mineral levels and max flow? That could impact your plans, better to find out now.

Utilizing the clay soil you have is key. Test it, make sure it really is super high in clay particulate. Given that any seepage losses would be very problematic with your water situation, getting a tight seal is imperative. Building at the top of your land where the clay is would probably be good, as transporting enough clay to seal a pond that size would be expensive. And the underlying rocky/sandy geology is always a bit risky. If you wanted the pond on the lower part of your land, a liner is not as bad an idea as some would make it out to be, especially for small ponds where water losses are critical. When you have a thru-flow of water from a stream, losses are not noticed and benefit the adjacent ecology. But your situation is different, and seepage could be a big issue.

There are evaporation calculations that you can do, either by searching for your climate online, or through a local gov agency like NRCS. I think evaporation will be one of your smaller concerns, but still one to evaluate. Less surface area is always better, but you dont really want your banks sloping steeper than 3:1 for safe entry and exit of both people and wildlife. And a circular pond isnt necessarily the look you would want. For a 1/4 acre pond, I would aim for something like 10+ feet of depth. I think it is pretty inevitable that the pond level will fluctuate quite a bit through the year, so consider the aesthetics of that if appearance is a major concern.

Keep up the research, the project will not be easy but it will be worth it! Ponds are one of the most satisfying features of any healthy landscape.

I think seepage will be a bigger problem than evaporation. I had a few small ponds and aboveground cisterns in Georgia, all lined with variations on the "carpet sandwich" theme and found that at most they might lose a few inches in the course of an average summer. In the West it's another matter. I filled some 300 gallon plastic tanks in March, and they are already about half gone! Unless you make the pond in the clay area or are willing to move a large amount of clay to the pond site, I would plan to line the pond somehow.

I think I'd try a pond of about 500 sq. ft. which is 1/20th the size of a quarter acre. Even then, I'd proceed only if a builder thinks it is at all practical. Have you seen other ponds done in the way you propose ?

If it works out, make the next one bigger.