I know that this web site isn't intended as a survivalist forum. Can anyone suggest one that is?

I want to make a water storage pond on a hill above my garden. My neighbor has a front loader/backhoe so digging it will not be a problem. I was thinking about a BIG pond, maybe 200,000 gallons. Does anyone know what kind of waterproofing would be cheapest and most effective? I do not want to pay a lot for this muffler. This pond is dual purpose: It will supply my garden with water during the dry summer and prove power because the pond will be a good 100 feet above the level of the garden. I would also like to use it to raise fish, but this is not an absolute requirement. If the pond isn't for fish, then I can cover it so as to keep off the sun. What material would be the way to go? I looked up some pond liners online and they were insanely expensive. Anyone have any suggestions?