Exact evaporation rates are difficult to estimate because there are so many atmospheric variables. However, 1/4" per day of losses during unseasonably warm weather (which is also usually dry) seems to be about right.
Was the water level in your pond higher than in the adjacent pond? If so, then there may be a slight leak through to that pond.
That should NOT be a problem if the old pond usually stays nearly full. You might place a water gauge staff in both ponds. After the next big rain fills your pond, mark both pond levels. Evaporative losses should be roughly the same from both ponds. However, if yours is leaking, it should go down faster. If yours is just leaking to the adjacent pond, then it should go down faster UNTIL the pond levels equalize, and then your rate of water loss should slow substantially.
Have fun with your new pond!
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