A lined pond won't take a lot of effort to keep clear.
SolarKey has cheap, submersible solar fountain pumps that can lift water 4-5 feet efficiently. The SBL1502 can easily move 1000 gallons per day, and could slowly circulate the water to a sand/gravel/bio filter, where nutrients, plankton, and other particulate matter would be removed. The right bio filter could just about make it drinkable. If 1K gallons per day isn't enough (and probably isn't), you can always add more pumps.
I use a smaller pump from SolarKey to move water to and from my bait pond. It chugs along relentlessly. The pump motor is brushless, and should last for years.
