I am interested in building a pond near my home in Maine. Unfortunately, water supply is limited, so I was curious to see if it would be possible to maintain a pond without having to manually refill it using well water. I found some resources suggesting the possibility of using rooftop collected rainwater for topping off a pond, but I wasn't sure if this would be sufficient, so I created a spreadsheet to determine feasibility.
The results of this spreadsheet appear too optimistic for me to believe. Using average rainfall/evaporation data for my area, an assumption of 1 gallon leak per hour, and inputs for the dimensions of the roof and prospective pond, the water level seems to stay completely full without any intervention all year round.
Is this possible? Have I missed anything in my calculations? I'm thinking of using a rubber liner, but mostly I'm investigating if this is possible in any way first before looking at specifics.