At least 44% of the island's residents don't have access to potable water, according to the Defense Department.
Gov. Ricardo Rosselló told CNN that crews are trying to restore water supplies for residents. But it hasn't been easy.
"In terms of aqueducts, we have been able to restore only 50% of water, because the majority of water in Puerto Rico also depends on electric generators," he said on Wednesday.
Generators need fuel, which is on short supply.
Elí Díaz-Atienza, executive vice president for Puerto Rico's Aqueduct and Sewer Authority, told San Juan-based WKAQ radio the island's water facilities were significantly damaged during the hurricane. He said his agency was working to water distribution sites for residents. Díaz-Atienza said his water restoration plan includes using trucks to deliver water to residents in the island's rural areas.
"We understand the frustrations of the people... We would love it if everyone had water right now," he told the radio station.
As government officials work to rebuild water systems throughout the island, the water situation has become dire with each passing day.
The World Health Organization says a lack of safe drinking water and suitable sanitation could lead to significant health risks, some of which include diarrhea, hepatitis, malaria and malnutrition.
After a natural disaster, the Centers for Disease Control and Prevention advises residents to listen to the local officials to find out if their water is safe to drink. The CDC suggests boiling water, using disinfectants or a filtration system to sanitize water.
The CDC says bottled water is the safest choice.
Although water and food supplies have been delivered to residents stranded on the island, San Juan Mayor Carmen Yulín Cruz told CNN more can be done.
She said thousands of shipping containers with food, water and other supplies are sitting at the Port of San Juan due to "a jurisdictional situation."
FEMA Director Brock Long said supplies are arriving in Puerto Rico, but delivering them to cities is the issue
The hurricane wiped out roads and devastated the island's airports and shipping ports, which he said is hampering delivery efforts. The federal government, Long said, has established distribution sites and is conducting airlifts to distribute supplies.
"It's not just possible to pick up the supplies and move it forward," he said. "That last mile is a coordinated sequence process to be able to get to the points of distribution ... As the supply chains come back online, we will be able to increase the amount of supplies that are going. But listen, we are not going to be able to move as fast as everybody would like us, or as I would like. But we are pushing everything that we have."