Mushrooms with gills shouldn't be rinsed with water because water gets trapped in the gills and the mushroom also loses on flavors when rinsed. Professional chefs brush mushrooms with a mushroom brush. The problem is that commercially available mushrooms tend to be treated with pesticides and you really don't know where they came from. So, in those cases, I recommend taking them through some running water quickly and then pat them dry very well and carefully so as to not damage your mushroom. If your mushrooms are just muddy, I recommend wiping them off with a damp clean cloth. I also recommend only buying mushrooms that are labeled as pesticide-free. Organic (or Bio) doesn't always mean no pesticides because every country has different labeling laws.