When torrential rainfall in August 2022 pushed the Pearl River in Mississippi to surge well beyond its banks, floodwaters spilled into the suburbs of Jackson and led an already-hobbled water treatment plant to fail.

It was the final stroke in what experts described as a yearslong issue in the making, which eventually left tens of thousands of residents in the city without clean drinking water for weeks.

What happened in Jackson, experts say, is a bellwether for what's to come if America continues to kick the can down the road in addressing its aging and crumbling water infrastructure. The climate crisis threatens to make those issues even more pressing.

When sea levels rise, summers become hotter or heavy rains lead to more flooding, the country's water infrastructure -- largely built last century and only designed to last roughly 75 years -- will be more strained than ever, threatening a system vital to human life.

At the rate our climate is changing, America's water infrastructure is not equipped to handle the challenges to come, said Erik Olson, the senior strategic director for health and food with the National Resources Defense Council.

"America's water system relies on last century's infrastructure that often can't protect our health from hazardous contaminants," Olson told CNN. "And our outdated system is completely unprepared for this century's challenges of intense heat, drought and flooding."

The American Society of Civil Engineers gave America's drinking water infrastructure a C-minus in its 2021 report card. And climate change-fueled extreme weather disasters promises a gauntlet of even tougher tests.

The 2021 infrastructure legislation signed by President Joe Biden includes about $30 billion for drinking water, and the 2022 Inflation Reduction Act another $550 million for water infrastructure. But experts say those figures are not enough to make up for decades of disinvestment and mismanagement across the country.

In Jackson alone, it could cost $1 billion to $2 billion to repair the water system, and the water industry estimates that the total nationwide costs will top $1 trillion. "Federal investments account for just a few percent of the total needs," Olson said.

To better understand the issue, CNN examined five cities or regions across the country that show signs of vulnerability under a rapidly warming planet -- from coastal flooding in New York to saltwater intrusion in California's groundwater.

Buffalo, New York

Buffalo water officials don't have to wonder too hard about its worst-case scenario. It basically happened last year.

A devastating winter storm dropped more than 50 inches of snow on the city in December, knocking out power, making roads impassable and killing 46 people in the area.

The high winds from the storm generated a phenomenon known as a "seiche," in which water from the west end of Lake Erie near Toledo was pushed east, creating high water levels and coastal flooding in Buffalo.

The blizzard and seiche flooding threatened to knock out power to Buffalo's water treatment plant, located precariously along Lake Erie. Thankfully, the plant has multiple backup sources, and the plant employees toughed out the storm, keeping the plant online and delivered clean water to residents. But Oluwole "OJ" McFoy, the general manager of the Buffalo Sewer Water Authority, said it was a "nightmare scenario" for the city and a warning of how rising water levels could impact its water infrastructure.

"(If) we don't have power, we can't do anything. And we've seen those high winds, especially those associated with many of these high lake levels, knock out power, and we've had to use our backup power as well," he said. "Everything for us is just about being resilient, but those things cost money, and you have to make sure that as part of your capital expenditure that you're building that resiliency into your system."

The non-profit organization Buffalo Niagara Waterkeeper has teamed up with the city on a study of the city's coastal resiliency. Climate change has made the flooding issues worse in recent years, as the average water level has risen and the lake no longer completely freezes over in winter.

"That perfect storm -- flooding, coastal storms, lack of ice coverage, fluctuating lake levels, erosion -- all of that is being exacerbated from the effects of climate change," said Kerrie Gallo, the deputy executive director of Buffalo Niagara Waterkeeper.

Prichard, Alabama

The Gulf Coast is no stranger to devastating storms. But in Gulf cities that aren't as populous or well-invested in, a hurricane could trigger a water infrastructure crisis.

Residents of Prichard, Alabama, believe their city -- a less than 10-minute drive from Mobile -- could be "the next Jackson," said Carletta Davis, president of the non-profit We Matter Eight Mile Community Association. From intensifying storms to leaking water lines that are never addressed, as well as racial injustice, the issues they face are multifold, she said.

Prichard's infrastructure on average leaked 56% of the water coming in from reservoirs each month from April 2021 through November 2022, according to a report from the Alabama Department of Environmental Management.

"This water system has completely failed," Davis told CNN.

"Hurricanes are one of our biggest threats, along with heavy rainfall, coastal erosion and flooding," she said. "And when it rains, we have sewage overflows, buses can't even get kids from school to their homes, and the streets are completely impassable."

Prichard is a predominantly Black and low-income city, and the historical legacy of disinvestment and racial injustice remains baked into the decisions made for the city's residents, including repairing and upgrading its water systems, said Catherine Coleman Flowers, founder of the Center for Rural Enterprise and Environmental Justice.

"The problem we are seeing in Prichard is similar to the issues we see plaguing communities around the country," Flowers told CNN. "Failing water and sanitation infrastructure that hasn't been repaired in decades due to lack of funding and discriminatory distribution of public funds have led to issues that can spread diseases and threaten public health."

The impacts and financial burden of Prichard's failing and aging infrastructure then gets passed on to the residents in these communities, she added. Ramsey Sprague, president of the Mobile Environmental Justice Action Coalition, said it's just a matter of time until another storm hits the Gulf and shuts Prichard's entire water system down.

"We're staring down the barrel of a gun," Sprague said. "With these infrastructure challenges in cities like Prichard, there are whole populations that are teetering on the brink of total collapse that can't be easily addressed."

As of August, after years of calling on city leaders to solve their escalating problem, Prichard's water utility board began the process of eminent domain -- condemning residents from their homes so they can work to fix the water system. It's a move residents and community advocates are fighting.

St. Louis, Missouri

Lead pipes were commonly used in water systems across the US until they were outlawed in 1986 due to the danger of lead poisoning.

But in cities like St. Louis, which has seen a stark population decline since its heyday in the mid-20th century, some of these older lead pipes remain and have the potential to leech the toxic chemical into the water supply.

Even low levels of lead exposure are dangerous for children and can damage the blood cells and nervous system or cause other disabilities. The Environmental Protection Agency has called lead poisoning the "number one environmental health threat in the US for children ages 6 and younger."

The state of Missouri is fourth in the nation in terms of lead service lines per capita, according to data from the NRDC.

St. Louis has tried to remove these lines -- but doesn't know for sure where they all are.

"Just because St. Louis is an older city and it was a very commonly used plumbing material, especially for the smaller lead service lines from the water mains into people's homes, they were just very widely used," said Rachel Rimmerman, the director of business and outreach at the Water Access, Technology, Environment and Resources Institute at Saint Louis University. "It also wasn't very common practice to have an inventory of where those lines are."

Furthering the problem, climate change has led to more intense flooding and storms, and that has the potential to damage older, weaker water systems like in St. Louis, said Jason Knouft, a biology professor at Saint Louis University studying the impact of climate change.

"These things were constructed based on a smaller population and less intense storm events, and so as we move forward ... it's a broader problem with our water infrastructure," he said.

The issue has not gone unheeded. The massive 2021 infrastructure law includes $15 billion for lead service line replacement, according to the EPA.

Central Coast, California

Roughly an hour from California's Bay Area and less than a mile from the Pacific Ocean, Kelli and Tim Hutton purchased a half an acre property in the Central Coast town of Moss Landing last summer.

As with many others living in the area, they heavily rely on their private well for water.

After moving into the new home with their newborn baby, the Huttons heard other residents were concerned about high levels of saltwater intrusion, being so near the ocean. Rising sea level and California's whiplash weather have been impacting their water table, with seawater seeping in and causing pipes to corrode, making water undrinkable.

The threat of saltwater intrusion increases during a drought, which California is facing more of under a worsening climate crisis. When water supply is low, groundwater is over-pumped from coastal aquifers, disrupting the balance between inland freshwater and ocean water. As groundwater levels drop, saltwater seeps in and fills in the gaps in the soil where freshwater used to be.

It's not just drought. Storm surge and floods can also push saltwater far inland, according to the US Department of Agriculture. And with climate change increasing the potential for weather whiplash, dramatic shifts in periods of drought and high precipitation, in California, saltwater intrusion is becoming an increasing threat for people living along the coast like the Huttons.

"We really need to be proactive about finding ways to conserve our water as far as we're using it, whether that's recycled water purposes or drip irrigation," Tim said. "If we don't take care of it now, it's only a resource that's going to be with us for so long. If our table starts drying up, then we're going to be out of luck."

This part of the Central Coast is also surrounded by farms that have been using decades' worth of fertilizers which turn into toxic chemicals. For the Huttons, water quality tests show their private well actually contained nitrate levels five times the government's safe level for drinking.

"It's been pretty uncomfortable and kind of nerve-wracking, especially when it's like bath time and babies open their mouths when they're in the water," Kelli told CNN.

San Juan, Puerto Rico

Hurricane Maria wreaked havoc on Puerto Rico in 2017, leaving much of the island territory without power for month. And because Puerto Rico's water infrastructure relies heavily on the electric grid to operate, many residents were left without running water in their homes for just as long.

It gave a glimpse of how frail Puerto Rico's water system can be during an extreme weather disaster. But what makes the infrastructure even more vulnerable is its lifespan and disrepair, said Félix I. Aponte-Ortiz, an urban environmental planner and retired professor at the University of Puerto Rico.

"The transmission is fragile, and it's very subject to hurricane and huge precipitation," Aponte-Ortiz told CNN. "Every time we have a hurricane or a tropical storm, we have a problem with the electric system. The potable water system is the same; they're very old."

Estimates show that 60% of the city's water mains in San Juan -- which sources its water from both reservoirs and groundwater aquifers -- are over 50 years old, according to a 2019 report by the Puerto Rico Aqueduct and Sewer Authority. These older pipes are more likely to leak and break, which could trigger water shortages as well as water quality problems.

The Natural Resources Defense Council along with local groups released a report in 2017 that found nearly all of Puerto Rico's residents were drinking water from systems that violated the Safe Drinking Water Act, and that almost 70% of people on the island were served by water sources that violated the policy's health standards -- the highest of any state or territory, NRDC's Olson said.

Water repairs and upgrades have always been costly across the country. But in Puerto Rico, every extreme weather event compounds the burden of the historical legacy of federal disinvestment in US territories, making repairs an even greater struggle.