Can you take a picture of it? Are the lines dry or wet and do they come all the way down the side of the heater? Is there any water in the pan? If there is no moisture anywhere, I'd keep an eye on it DAILY! If it come from one of the 3 connections (hot & cold pipes or relief valve), it might just be not tight. However I would not try to stop the leak by simply tightening the connection, that has caused many a flooded home. Just curious, what is the water pressure at your cabin? Lastly, how old id the heater?
I have done that (sewer only) not water lines. But if tere is a septic tank it usually does not reveal anything. If you suspect roots, it can reveal them or other blockage. Sometimes you can see disconnections of waste water pipes.
Could also be heat recovery which would come off hvac unit. Freon runs through small heat exchanger (breadbox size) which circs water over to water htr and could enter through htr drain connection. Pipe sz 1/2" sometimes. Had one at my place and went htr blew took whole thing out, was leaking at every fitting and heat exchanger looked shot.