Mushrooms grow low to the ground so they will usually carry a bit of dirt when sold in stores. However, I never wash mushrooms because they will get waterlogged! To clean them, use a damp paper towel or a soft mushroom brush to wipe each mushroom to remove any dirt. If you do want to rinse them, rinse them with cool water and pat them dry really well with paper towels. Do not soak the mushrooms. Mushrooms absorb water like sponges, so they won’t brown nicely when cooked