MEMPHIS, Tenn. - In Memphis, our water is a source of pride. Environmental scientists say it is some of the best in the world.

Our drinking water comes from the Memphis Sand Aquifer, which sits hundreds of feet underground.

The aquifer is made up of a mixture of water and sand. The sand helps filter our water.

On top of the mixture is a confining layer made of clay which protects our aquifer from contaminants.

Scientists have found there are holes in that confining layer called breaches, where our aquifer is less protected.

"When you drill through it, if all you hit is sand or conductive material and never the clay - that is a breach," Brian Waldron, the head of the Center for Applied Earth Science and Engineering Research (CAESAR) program at the University of Memphis, said.

Waldron's mission is to find the breaches.

Scientists have confirmed at least five breaches in Shelby County and are investigating several others.

"The fact is if a contaminant can get through a breach, then it's in the Memphis aquifer, and unfortunately we don't know about it until it hits an actual production well," Waldron said.

A production well pumps water from the aquifer to deliver to our homes. That water is tested frequently to make sure it's safe.

It can take decades for chemicals from the surface to filter down hundreds of feet to the aquifer.

"If we can identify where these breaches are and then look at the land use practices both now and in the past, we can get an idea of what could be coming, before it actually hits," Waldron said.

The Memphis advocacy group Protect our Aquifer works to protect our natural resource. Sarah Houston is the executive director.

"Pollution is slow moving, but as you know Memphis is an industrial town," Houston said. "We have had manufacturers here for over a century and before the 1970s, before the clean water act, a lot of that pollution was just dumped or buried underground."

If you overlay Memphis' toxic sites on top of the known aquifer breaches, it highlights the areas of most concern.

One is the TVA plant in Southwest Memphis - tons of coal ash filled with arsenic, mercury and cadmium.

Another is the old Defense Depot, where chemical weapons like mustard gas were buried and where pesticides that are now banned were used frequently.

Another area of concern is south of the University of Memphis where a former dry cleaners dumped chemicals for decades.

"Whenever you get contamination and water it is not easy to clean up," Houston said. "Picture your bathtub. And you drop some dye in it, it starts to spread a little by little. You can't just scoop that dye out and that's what's going on on in our aquifer is when you get some pollution it starts to spread out underground. You can't see it, but we know there is an issue there."

FOX13 Investigates has shown you the project to remove the toxic coal ash from the TVA site to a landfill in southeast Shelby County. That work will take nearly a decade.

We've also shown you the old Defense Depot in South Memphis, which the government says is clean now but continues to monitor.

Work continues to extract chemical vapor at the former cleaners site on Southern Ave.

For now, there's no way to repair the breaches, so those areas remain most vulnerable.

"We can't take it for granted anymore," Houston said. "We can't expect that it's going to come out of our tap perfectly clean forever unless we get involved and do something and demand that."

It is important to point out that right now, environmental scientists say, our water supply is still very clean and they haven't seen any widespread contamination.

They are working to discover and treat contamination before it hits our aquifer.

Advocates say there are some simple things you can do to help stop groundwater pollution.

Those include not dumping chemicals down drains or on the ground and keeping lids of waste dumpsters closed to prevent rainwater washing materials out of them.