Both aluminum and copper are not that reactive to water. You can clean them with water, but you want to dry them off quickly afterwards. A hair dryer can work for this. The problem is actually, if you can't get it with compressed air, water may cause the debris to turn muddy and stick harder. I personally, used to blow them out with a compressor (used in automotive applications.) In this case, it's important to gently compress the cooler in your hands so that fins don't come flying off. (If you are bending fins, you are doing it too hard. You just need to hold them in place.)