At least once a week though a quick soak daily is good if you have the time and can manage it. They should be misted daily and some people have a shallow area of water (a nice rock to keep it in place can be a good idea, lol) they can mess around in that you clean daily (often more than once) in the habitat and can help with humidity a bit. Here is the link to the green iguana society with lots of care information.
www.greenigsociety.org
www.greenigsociety.org
