I have some rain barrels in my yard. After a certain amount of tinkering, they collect rain water well. However, I notice that a day or two after the rain, most of the water is gone. I've checked for leaks in the barrels and their hoses without finding any. I also moved the rain barrels out of direct sunlight as much as possible. Is it normal to lose so much water this way? Is it evaporation, or something else?

Besides the rain barrels, I have some buckets to do rain catching. These do not seem to lose water at the same rate. What gives?