Yeah, that's it. Water itself doesn't carry any loose electrons as H2O is a stable compound, therefore it doesn't conduct electricity. The problem with water is that it's an excellent solvent of minerals, so very quickly in contact with PCBs etc., it will dissolve some minerals from dirt, surface coatings etc. which will provide loose ions and electrons, and then it'll start conducting. Even a beaker of pure water left open to the air will quickly become impure as it absorbs molecules from the air.
