my family and i have just returned from a month long trip to discover a leak in our basement ceiling. our first instinct was to check the waterline behind the refrigerator (because the leak seems to be coming from behind our fridge on the main level) but we found that it was dry, except for the corner near the wall. The waterline is dry. We are now suspecting that the leak is coming from a bathroom on the second level(possibly from the shower line?). conveniently, near where the water is dripping in the basement, we have an access port for the water supply (a little cut out box in the ceiling under the fridge). we looked inside and it seems that the water is coming from where the HVAC is in the wall behind the refrigerator.
we are wondering if anyone knows where this leak could be coming from? or if there is a way for us to fix it ourselves? is it possible that a leak in a basement ceiling could be coming from a bathroom on the second level?

I would check first that the condensate drain for the AC isn't backing up, and second that the condensate isn't coming out of the unit itself and is going to the drain. Commonly in the summertime, condensate drains build up a snot looking mess from all the mold and pollen and whatnot in the air. You can probably use a small snake or even the end of a garden hose shoved down the drain to break up the clog if that is what is happening. Do not pour anything into a backed up drain, but if the line opens, pour water down it to verify that it is open, then I would add a cup of bleach to the drain to destroy any remaining 'snot'. Double check in an hour to make sure it is still open.

Any water using fixture in the area is suspect, but KCRoto offers the first place to check according to your question. Best of luck.

If the leakage is in water supply pipes then the best way to identify the source of the leakage is as follows:
Plug all the water supply points, fixture, shower head with the help of end plugs in the area of leakage.
Isolate that area from the water mains with the help of stop cock / ball valves.
Mix approx 17oz (500 gms) synthetic dye / food color in approx 10 US Gallons (40 liters) of water.
Pump this colored water with the help of testing kit / pressure pump in ur water supply lines.

Pump till 4-6 Bar of pressure is achieved and leave it over night.
Next morning, try to identify the spot from where the color is coming out.
If ur able to find it, then Bingo.
If not then ur leakage is probably in the drain pipes or somewhere else, for which we would recommend to call your local plumber to identify it.