Almost three years after wildfires tore through Maui, HI, residents are still rebuilding and recovering. Now, Hawaii is reeling from a natural disaster again. This time, it's water.
Back-to-back storms in March brought historic flooding to Maui, Oahu, and communities across the Hawaiian Islands—the worst the state has seen in over two decades.
The damage was staggering: Floodwaters lifted homes and cars, collapsed a condominium building in Kihei, and prompted evacuation orders for thousands of residents. More than 200 people were rescued from the water. Gov. Josh Green put the statewide damage estimate at over $1 billion.
Now, as the water recedes, a second crisis is emerging inside the walls of flood-damaged homes—one that's invisible, fast-moving, and potentially far more lasting than the floods themselves.
Imagine 3 million Olympic-sized pools of water falling on you
The storms that struck Hawaii weren't ordinary bad weather. They were back-to-back kona low systems—subtropical cyclones that drew moisture up from the tropics and stalled over the islands. More than 2 trillion gallons of water fell over 14 days, enough to fill 3 million Olympic-sized swimming pools. Rainfall in some areas reached 3,000% of normal levels for this time of year.
The first storm brought hurricane-force wind gusts and up to 62 inches of rain to Maui. The second triggered what Honolulu Mayor Rick Blangiardi called a "rain bomb"—a stationary storm cell that dropped 2 to 4 inches per hour over Mānoa and Palolo valleys on Oahu, on ground already saturated from the week before.
"Anything that was 4 feet or below, it is just completely wiped out," said one North Shore resident who helped neighbors dig out. "Cleanup is going to take months."
For homeowners, that cleanup phase is where the next danger begins.
The mold clock starts immediately
In videos posted to Instagram, chiropractor Katie Gravesen documented her flooded home office on Maui in real time: tearing up flooring, pulling drywall, running fans and an air purifier after she couldn't find a dehumidifier anywhere on the island.
Gravesen's footage captures what countless Hawaii homeowners are now facing: the urgent work of drying out a space before mold takes hold.
That urgency is well-founded. According to Michael Rubino, mold and air quality expert and founder of HomeCleanse, the window for action is tight.
"Mold spores can begin to grow within 24 to 48 hours when provided with moisture," he says, "and many bacteria can do the same."
Once established, mold particles such as spores, fragments, and mycotoxins become airborne, spreading through the home every time the HVAC system kicks on or someone walks across the room.
"That's why mold in one area can impact the health of the entire home," Rubino says.
The mistakes homeowners make during DIY cleanup can make things worse.
Rubino warns against addressing only what's visible. Water-damaged material inside walls, under flooring, in crawl spaces, and within HVAC systems can harbor microbial growth long after surfaces appear dry.
Fans move air, but dehumidifiers actually pull moisture out of it. With dehumidifiers reportedly sold out in parts of Hawaii, homeowners should get one as soon as supplies allow.
And floodwaters themselves introduce contaminants that settle onto surfaces and keep circulating in the air long after the water is gone.
The Hawaii Department of Health advises removing all floodwater, dirt, and debris as quickly as possible; keeping walls open to allow complete drying; and discarding porous materials—carpet, padding, mattresses—wet for more than 24 to 48 hours. Wear waterproof boots, heavy-duty gloves, an N95 mask, and sealed safety goggles. Don't reenter until electricity is shut off, gas lines are secured, and the structure is deemed safe.
Of course, you may also want to bring in help. Rubino's rule of thumb for when to go beyond DIY is clear: Mold growth exceeding 10 square feet calls for a professional. So does any situation involving sewage-contaminated floodwater, underlying health conditions, or whole-home flooding.
"Depending on the type of event, it can bring in a host of bacteria, molds, and toxins that can cause serious illnesses," he says.
What the damage means for your property
The cleanup costs are only part of the financial reckoning Hawaii homeowners face. Flood damage carries lasting implications for property values, insurability, and the ability to sell—and the insurance landscape was already complicated before the storms hit.
"Hawaii flood insurance is a mess of conflicting data," says Sam Meenasian, vice president of Sales & Marketing Operations at USA Business Insurance. "FEMA maps are outdated, private carriers are pulling out, and homeowners are caught in the middle. I've seen properties that haven't flooded in 50 years suddenly underwater because of development upstream."
Buyers who want to protect themselves, Meenasian says, should get an elevation certificate, check their area's Community Rating System score, and confirm their standard policy covers water damage.
Low-risk homes have been appreciating faster than high-risk counterparts for years, and that divide has widened significantly since 2022—a trend Realtor.com® economists tie to rising buyer awareness of flood risk. Sellers face disclosure obligations on top of that, as failing to disclose known flood damage can create significant legal exposure.
Hawaii homeowners face new flood map guidelines on top of everything else. Updated FEMA Flood Insurance Rate Maps for Oahu take effect June 10, 2026, the result of years of study of streams across the island, many evaluated for the first time. Properties newly mapped into Special Flood Hazard Areas will face new coverage requirements, and owners with federally backed mortgages may be required to carry flood insurance for the first time. Homeowners who don't act risk having a policy force-placed by their lender—typically at a higher cost than shopping for coverage independently.
For anyone buying or selling in Hawaii right now, the steps are clear: Check your flood zone designation at FEMA's Flood Map Service Center, review your insurance before June, and if you're in a flood-damaged home, don't wait on the mold. The damage compounds quietly, and so does the cost of ignoring it.
