Lesson 01

Meet the Aquifer

Under Memphis, stacked like pages of a book, are layers of sand and clay that reach down almost a quarter-mile. Your drinking water lives inside one of them.

Scroll to travel down through each layer — from the surface to the deep backup aquifer 400 meters below.

Tip: the 3D view on the right updates as you scroll.

0 – 50 feet · Quaternary

Where the rain starts

The top layer under Memphis is loess — wind-blown silt deposited during the last Ice Age. It's what forms the Chickasaw Bluffs that give Memphis its elevated shoreline above the Mississippi.

Rain that falls here begins a long, slow journey downward. A single raindrop might take decades to seep through this first 50 feet.

50 – 150 feet · Alluvium

The shallow aquifer

Below the loess sits the Mississippi River Valley Alluvial Aquifer — river-deposited sand and gravel, extremely productive for agriculture.

But it's close to the surface, which means it's close to whatever pollution is happening above. And it sits directly on top of Memphis's drinking water.

150 – 350 feet · Clay

The clay shield — and its holes

Between the shallow aquifer and Memphis's drinking water is a 200-foot-thick wall of clay called the Upper Claiborne Confining Unit (UCCU). When it's intact, it stops contamination cold.

But in places, it isn't intact.

350 – 950 feet · Memphis Sand

Your drinking water lives here

The Memphis Sand Aquifer is a 600-foot-thick layer of pure quartz sand. It's where 100% of Memphis's drinking water comes from — over 200 million gallons a day, from 160+ MLGW wells.

The water is so clean that MLGW only has to add a small amount of chlorine and fluoride — no filtration plants, no coagulation, nothing like what most cities need.

950+ feet · Deeper aquifers

The backup, and the floor

Below the Memphis Sand is another clay layer, then the Fort Pillow Sand — a deeper, even more ancient aquifer. Some West Tennessee towns use it as their main supply. Water here has been underground for over 10,000 years.

Under that lies the Porters Creek Clay — the geological "floor" of the whole system. Nothing flows through it. It's why the aquifers above stay pressurized.

Why this matters

This whole stack — the clay, the breaches, the sand, the pressure — is why Memphis has some of the best tap water in the country. And it's why advocacy matters: everything that happens on the surface eventually reaches the water below.