Lack of water and heat definitely cause impaction. They need both to be able to pass the food. I had one of my iguanas get impacted once with the zoomed iguana diet because of this when I first started feeding pellets. I had many iguanas in the cage at the time and I hadn’t taken into consideration that the dominant female had chosen her spot right next to the water bowl. She wouldn’t let the lesser female near it. I was able to reverse the impaction by forcing feeding her a few CCs of water per day along with a little bit of mineral oil (in both ends) until she was flushed out. I seperated them and added more watering stations after I figured out what was happening. I feed mainly pellets now and she has never had a reoccurrence.