His message to the world: I'm alive, and I'm American.
It worked, if temporarily. Helicopters came. So did a tarp, food and bottled water.
Yet little else has changed. His roof is still missing, as are some walls. He and his cat, Tipo, sleep in the kitchen. When the wind blows at night, rain soaks them. The power is out, as it is for roughly 3 million Puerto Ricans, or more than 80% of the island's residents. More than a third of households in the US territory, including much of Sostre's community, are without reliable drinking water at home. That's roughly 1 million American citizens.
One month after Hurricane Maria, these realities are starting to feel less like an emergency and more like the new way of life -- a nightmarish loop that resets each day the sun rises.
"You wake up and it's this mess as far as the eye can see," Sostre told me.
Much of the island feels like it was hit by a storm yesterday
The US government says it is committed to helping Puerto Rico but is confronted with challenging circumstances, including some roads that are narrow, muddied and impassable for large aid-delivery vehicles. There also are pre-existing problems with power and water systems. Puerto Rico is "an island sitting in the middle of an ocean ... a very big ocean," as President Donald Trump said on September 26, making Hurricane Maria more distant than two other recent storms that hit the US mainland, Hurricanes Harvey and Irma.
After traveling the island for three days, however, and conducting interviews with residents and federal officials and experts, it's clear the level of suffering is far outpacing relief.
Much of the island feels as if it were hit by a storm yesterday, not one month ago. Mountains are covered in branchless trees, stuck in the dirt like the walking sticks of giants. Power lines are tangled about like spaghetti dropped from the sky. Sheet metal from roofs and fencing has been turned into floppy strips of chewing gum, scattered on the hills. Not only are people such as Sostre exposed to the elements, but supplies of clean drinking water are woefully inadequate and environmental health experts fear a public health emergency could be brewing.
On Tuesday, the Federal Emergency Management Agency, or FEMA, said it had 1,700 personnel deployed in Puerto Rico and the US Virgin Islands, which also were hit by Hurricane Maria. Yet nearly 2,600 FEMA staff -- about 900 more -- remain deployed to Hurricane Harvey, nearly two months after that storm hit the Gulf Coast of the mainland United States.
In their defense, FEMA officials point out also that 20,000 other federal staff and military have been deployed to respond to Hurricane Maria.
"(P)lease understand that every disaster is different geographically and demographically and there is no point of comparison from one to the other. Numbers are a snapshot in time for any given day; it is like comparing apples to oranges," FEMA said in an emailed statement. "Please note that numbers do not save or improve lives, missions and progress do; for example, (Texas) may need more people to support housing, while (Puerto Rico) may need more generators and poles to support the grid."
Others see it differently.
"I thought we'd learned our lesson after (Hurricane) Katrina where the response was awful, both carelessly slow and incompetent," said John Mutter, a professor at Columbia University and an expert in international disaster relief. "In Puerto Rico, it doesn't look like we've learned anything at all -- or we just don't care."
'If I don't drink water, I'm going to die'
The situation is particularly bad when it comes to water.
There are 3.4 million people in Puerto Rico, and about 35% of households were without access to safe drinking water as of Tuesday, according to government estimates. The World Health Organization says each person needs at least 2.5 liters per day for drinking alone, with a recommended daily allotment of up to 15 liters per day including basic cooking and hygiene.
Yet FEMA has provided 23.6 million liters -- 6.2 million gallons -- of bottled water and bulk water since the storm hit on September 20, said Justo Hernandez, FEMA's deputy federal coordinating officer. That includes water delivered to hospitals and dialysis centers, he said.
That's only roughly 9% of the drinking water needs for the entire territory.
It's an even smaller fraction if you include basic cooking and hygiene needs.
"The potential for cholera and diarrheal diseases is quite high" without bottled water, said Mutter, the disaster recovery expert at Columbia in New York, who recommended the WHO standard. "What you will get is contaminated wells and surface water. It's a situation where you really should be drinking bottled water. If you can't get bottled water ... that's trouble."
Volunteer groups and nonprofits also are helping with supplies. FEMA says it has distributed drinking-water purification tablets and deployed six mobile-filtration systems. And there are efforts to distribute water-purification tablets and to tell locals who can't find bottled water either to boil the water or add bleach or water-purification tablets.
But many residents remain desperate, week after week, for drinking water.
Lines for water -- potable or not -- are long in many parts of the island. Rumors of contamination are rampant. Even as some taps turn back on, residents worry about drinking from faucets, which sputter and, in some locations, produce hazy liquid. Autoridad de Acueductos y Alcantarillados, the water utility in Puerto Rico, says on its website that residents should boil the water and add bleach even after service is restored.
In Dorado, near the capital, San Juan, people are so desperate for water they've turned to a federal hazardous-waste site in search of something to drink. CNN has reported that people are breaking through a fence marked "danger" to pull water from a Superfund site
in an area known to be contaminated with industrial chemicals linked to cancer. It's unclear if the wells are unsafe for public health; the Environmental Protection Agency is conducting water tests on wells on the Superfund site.
"If I don't drink water, I'm going to die. So I might as well drink this water," one resident said.
'There is a public health crisis here'
One afternoon, I met Wilfredo Santiago while he was collecting water from a spout along Highway 10. The area smelled something like a pet store, and Santiago told me there likely are dead squirrels, rats and horses in the hills.
Santiago knows it may be unsafe, but his 9-year-old daughter bathed in the water stream while he filled up a number of plastic bottles with the liquid. A line of cars waited to do the same. He took the water home to an apartment complex in Utuado, an interior city. On the floor in the kitchen, there were 37 jugs of the stuff, bottled in containers meant for Sprite, Pepsi and cranberry juice. The family collects water from a gutter to flush the toilet. There's no running water here, and bottled water is expensive and hard to come by, he told me. The grocery store in town had none. Deliveries to the area by government officials come infrequently, he said.
Across the street is the municipal emergency management office, which helps distribute FEMA aid. Héctor Cruz Cruz, its director, told me everyone in that complex is fine -- they all get bottled water delivered through the complex's manager. He disputed the claims of Santiago and about a half-dozen of his neighbors who said they are short on water and often struggle to find it.
"It's dangerous," Santiago told me, referring to drinking and bathing with water from the mountains, "but we have no choice."
All of this is concerning to public health experts.
"Our biggest worry is that as people get desperate and sort of give up on safe water sources that they are going to rely on things like streams and pipes that just come out of a spring or a mountain," said Erik Olson, head of the health program at the Natural Resources Defense Council, an environmental group. "It's just really a desperate situation."
"There is a public health crisis here," Catherine Kennedy, a vice president at National Nurses United, said from Puerto Rico. "They need water. And we haven't seen much of FEMA."
'I step out of my bed and there's water'
Hernandez, the FEMA official, said this relief effort is "a marathon," not a sprint.
But President Donald Trump already is emphasizing the finite nature of federal attention.
"We cannot keep FEMA, the Military & the First Responders, who have been amazing (under the most difficult circumstances) in P.R. forever!" Trump tweeted on October 12.
Carmen Rivera Rodriguez, a 55-year-old resident of "P.R.," didn't see that tweet. She has heard next to nothing about Trump or the federal response to this storm. When we met outside a supermarket in Comerío, about 20 miles southeast of Sostre and his American flag, she told me she hasn't even been able to reach her son in the mainland United States because there's virtually no cellular service here -- 75% of antennas are down -- and she doesn't have a car.
Rivera was wearing a cast on her left arm.
She fell while trying to sweep rain out of her living room.
That was October 11 -- 21 days after the storm.
Rivera invited me to her home, which is on a cleared and accessible road on the side of a mountain. When you step inside the house, your foot splashed in inch-deep water, sending ripples throughout the home across linoleum floors. This is what she was scraping with a squeegee when she slipped and fell. Her roof is gone, except for over the kitchen and a small garage, where she sleeps. And it rains most afternoons here, lately. "Just imagine. I step out of my bed and there's water. I go to the bathroom and I have to bring an umbrella," she said.
The same week Trump visited Puerto Rico, throwing paper towels to hurricane victims on October 3, Rivera told me she heard a truck driving by her home with loudspeakers blaring what seemed like good news: US government workers would be in town tomorrow.
The next morning, she said, she awoke at 4 and hitched a ride into the valley so she could apply for a tarp to stop it from raining indoors. Mold is growing on a baby picture of her now-grown son, which hangs on the plywood wall of her living room.
Her right eye is pink and puffy, which she figures is a symptom of being damp for one month.
She waited in line for hours and filled out a government form, she said.
As of October 15, 25 days after the storm, the tarp hadn't come.
FEMA has distributed 38,000 tarps on the island, said Hernandez, the FEMA official.
The need for roofing help is estimated at 60,000 homes, he said.
Puerto Rico is part of America and yet it isn't.
It's a territory of the richest nation on Earth -- a country founded in opposition to colonialism. It's a place where the federal government oversees a financial crisis and controls certain aspects of commerce and shipping, but where Americans can't cast ballots in presidential general elections, and where the island's one representative in Congress can't vote, either.
Sostre, the man who was trapped on the other side of a broken bridge, was right to fly the Stars and Stripes above his home and to say, "Soy americano," or "I'm an American."
Rivera, for her part, doesn't think much about the politics.
She only wants to stay safe and dry.
Nights have been the hardest, she said as darkness fell over her neighborhood and the island's coquí frogs began their electronic chorus. Rain splashed on the floor as she talked. The situation is so bad Rivera prays to God asking that if another storm comes, she won't survive it.
"I'm not ready to live through something like that again," she said, crying.
The truth is she's still living it.