As flood waters began swallowing roads and homes during Tropical Storm Harvey, panicked Houston residents did what everyone in the U.S. is programed to do in an emergency. They dialed 911.

But the emergency number struggled with record high call volume. At the peak of the storm, the service received around 80,000 calls in a 24-hour period. The Harris County area typically gets around 8,000 calls a day.

Some people were unable to get through at all, and those who did were put on hold while a recording -- which promised the call was being processed -- looped.

Desperate residents took to social media to post their addresses in the hopes that someone would get the information to the right authorities or a friend with boat. The requests went viral, leaving many wondering why 911 wasn't able to do more.

Like most 911 systems in the U.S., Houston's is based on outdated telephone network technology. There are 30 centers fielding 911 calls in greater Harris Country, where Houston is located. The emergency network is the largest 911 operation in Texas and one of the largest in the country.

It is more advanced than many — the centers can receive SMS text messages --- but it needs an overhaul to keep up with the smartphone age.

There is a plan in place to update systems across the country to something called Next Generation 911, which works over internet-based networks. It would make it possible to outsource 911 calls during a disaster like Harvey, and make it easier to process rich texts and better pinpoint locations.

Related: How social media is helping Houston deal with Harvey floods

Inside the Houston Emergency Center, call takers took turns pulling 12-hour shifts and sleeping in the building during the hurricane. Many employees worked in spite of their own personal emergencies.

There was no other option. Rerouting calls to 911 centers outside the system is not technically possible because of the legacy telephone technology.

"Moving calls around is really a physical [task]," said Trey Forgety, directory of government affairs at NENA, the National Emergency Number Association. "You have to go physically move wires, and it's nearly impossible to do it during a disaster."

Next Generation 911 systems would make it easy to quickly shift calls to other counties. It could also change how people communicate with 911 during a disaster.

Texting makes sense during a disaster when hold times are long and battery power is a precious resource. The greater Harris Country system received around 630 SMS texts this past week, up from 115 the week before.

But Joe Laud, administration manager for the Houston Emergency Center, said they prefer calls because it takes ten times longer to respond to a text.

Under the Next Generation system, people would be able to text photos, videos and other files to 911 instead of just words. Eventually the centers could hire video and photo analysts and text messaging specialists to process the requests.

Some of the issues 911 centers faced during Harvey are harder to solve. But the use of social media was an unexpected complication. Each tweet or Facebook post that was widely shared resulted in a high number of calls to 911 about the exact same, often outdated, cry for help.

"I'm still getting emails for high water rescues, but now we're finding out they're all duplicates," said Laud. "It's hard to coordinate anything, especially in the social media world."

The hope is that increased capacity for calls and other forms of communication will reduce the number of people posting publicly. That's preferable to trying to add social media monitoring.

"We're very conscious of the need to protect consumer privacy," said Forgety. "We don't want to be in the business of surveillance. It's a bit of a fraught area for us."

Related: Businesses donate over $113 million to Harvey relief efforts

They also don't want to be in the business of coordinating with amateur rescuers. Harvey saw an influx of civilian responders — people using their own boats, gear and smartphone apps to help people.

"Citizen responders in some ways are a great asset for our nation to have," Forgety said. "On the other hand, when they're not necessarily properly trained and properly insured, it's really difficult for the emergency response community to engage with them."

For now the industry is focused on less technical issues, like funding. The first stage of the switch to Next Generation 911 is expected to happen in 2020. It will take between $10 billion and $12 billion to update all the 911 systems in the country, according to NENA. The vast majority of 911 funding is done on the state and local level, though there is a pending federal grant program that could contribute $150 million.

Until 911 catches up to the technology on our smartphones, people can help call centers by following a few rules. Only call in case of an emergency, don't hang up and call again, and update your social media posts if you've already been rescued.

"I think everyone's got the message," said Laud. "Stay on the line and save 911 for true emergencies."