(CNN) What do you do if you're stuck in the floods in Texas and don't know how to get help? Here's what you should -- and shouldn't -- do, depending on your situation.

Call 911, but only for emergencies

The region's 911 centers are overwhelmed with calls right now. On Sunday, Houston 911 received seven times the number of calls it handles during an average day, the city's Office of Emergency Management said. So call 911 only if you have a medical emergency or need to be evacuated-- and keep trying to get through if the lines are busy.

You can also call one of five numbers for the Houston command center of the US Coast Guard if you're in danger and need rescue: 281-464-4851, -4852, -4853, -4854 and -4855.

If it's not critical, you can call a police non-emergency number

The Houston Police Department tweeted this notice Sunday : "If you need help leaving your home due to high water, but you are otherwise safe, you can call 311 or the HPD non-emergency number 713-884-3131."

Are you stuck in your house?

An evacuated Houston house shows where its residents broke through from the attic to escape.

Don't go into the attic if the home is taking on water, because you could get trapped if there is no exit to the roof. "Get out to where you can be seen and where we can respond and find you," Assistant Chief Larry Satterwhite of Houston police said.

But don't go far, because floodwaters can be extremely dangerous. The water is often contaminated with sewage and chemicals, and it can hide objects such as metal and glass. And in the Houston area, the water can also hide dangerous animals, including poisonous snakes or alligators.

It's safer to be stuck with a little water inside your home than to go outside, the Harris County Sheriff's Office advises residents.

Non-life-threatening water inside home is safer than going outside. Difficult & scary, but we'll get to you. Pls shelter in place. Be safe. https://t.co/9TXOwhtt9q — HCSOTexas (@HCSOTexas) August 27, 2017

Are you stuck on a road or highway?

Don't try to drive on the road if it's flooded. Even shallow water can cause drivers to lose control of their vehicles, and there's always a risk the floodwaters will rise -- and rise quickly.

If the floodwaters rise around your vehicle but the water is not moving, abandon the vehicle and move to higher ground, according to Ready.gov, a Department of Homeland Security website about disaster preparedness.

If the floodwaters are moving, don't leave your car. That might be the time to dial 911.

And beware of driving on bridges that are over fast-moving floodwaters, because that water can damage the foundation and make the bridge unstable, Ready.gov says.

Are you in a high-rise building?

If you are in a high-rise and need to shelter in place, go to the first- or second-floor hallways or interior rooms, the Federal Emergency Management Agency says -- but don't go to the highest floors. You want to stay on floors above floodwaters but the highest floors could be affected by wind.

Lastly, beware of hoaxes