Atlanta ? With drought tightening its grip on the Southeast, the Atlanta area’s reservoirs are almost down to the dregs – the dirtier, more bacteria-laden water close to the bottom – and it’s going to require more aggressive and more expensive purification.

Some communities are buying stronger water-treatment chemicals and looking into other measures to make the water drinkable.

The problem is that the water levels on Lakes Lanier and Allatoona, the main sources of water for metropolitan Atlanta’s 5 million residents, have descended almost to the “dead zone,” a layer low in oxygen and high in organic material – that is, dead and decaying plants and animals.

Even with standard treatment, the water at that level can have a strong odor, taste and color. State officials consider the water “suspect” at best.

“Is there water there that could be used? Yes,” said Carol Couch, Georgia’s top environmental official. “But it’s not exactly high quality.”

The dropping of the water levels into the dead zone won’t have a major effect on the city of Atlanta, because it does not draw its water straight from Lake Lanier, but from the Chattahoochee River, which is fed by Lanier.

By the time Atlanta takes its water from the Chattahoochee, it has been circulating for a while and has been exposed to more oxygen, and is thus not as dirty.