Mushrooms do not need to be watered like plants do. Instead we make sure the substrate in our grow bags that the mushrooms are growing in will have enough moisture to see the mushrooms through their life cycle. What mushrooms do like though, is Humidity in the air. Ideally you would use a humidifier to perfectly control the amount of humidity in the air for healthy mushroom growth. A cheaper option for beginners is to use a fine spray mister to spray water around the area that the mushrooms are growing to keep humidity levels maintained. Depending on the mushroom variety this is usually between 85%-95% humidity. This is the required level for many species of mushrooms. Try not to spray the mushrooms directly as it can damage them. Just around the base of the mushrooms to create a humid zone around the mushrooms.