(CNN) As Puerto Rico struggles with water shortages and a dire situation for many seeking medical care, the number of customers getting power off of the island's grid has declined, according to the latest available data and conversations with energy experts.

Last Monday, 15% of customers were receiving power compared with typical peak load. Today, that number was down to 13.7%, according to Department of Energy and Puerto Rican government status reports.

Puerto Rico Gov. Ricardo Rosselló said Sunday that he hopes to have 95% of power restored by December. The progress of the last week shows how difficult getting there will be, say groups working on the ground and energy analysts. The December goal "is indicative of the extent of the damage and the challenging terrain and geography," said Chris Chiames, a spokesman for Whitefish Energy Holdings, an energy company working with the Puerto Rico Electric Power Authority on the recovery.

From all sides, those trying to get the grid back up face challenges. Analysts who have studied Puerto Rico's grid gave several reasons the recovery is progressing so slowly.

1. Trying to put the electrical grid back together is a chicken and egg problem. Strange as it may sound, to get a grid working well, you need a strong existing grid to balance out problems that may occur. Electrical grids are self-serving systems that modulate power. Power plants run on synchronized intervals. When parts of a grid breakdown, it adds stress on the existing system.