I was researching the same question, so I am glad this came up. I lost one inch in one day, but that was when the pond top foot was at 90 degrees after a long hot spell, and then the temp and dew-point dropped with plenty of wind. I was very concerned for a leak. Now my losses are down to <1/4 inch a day now that it is cooler. Lost about 3" total from full pool with no rain in sight. It may work in my favor as I may be able to finish my dock up I could not finish last fall because the pond filled so quickly.

I have seepage on the middle of the back of the dam, but I cannot tell if it is from the pond or we covered a natural gas spring. It is FULL of gas bubbles which is somewhat common around here, but constantly wet to the point of sprouting cattails. The excavator was left scratching his head how our massive clay damn with a bulldozer width keyway could leak, so we are waiting to see what happens.

So as a test I filled a bucket with pond water so I could compare the two with the bucket next to the pond. The first inch loss paired up between the bucket and pond, but now the losses are differing. The 1/4 per day in the pond is 1/8 in the bucket. I am assuming that the bucket outer sides are dissipating solar heat without water loss so the water doesn't get as warm and the sides are blocking surface air flow. Really need an insulated bucket to better match the energy the pond receives and no bucket sides.