The ever-receding water levels at both Lake Allatoona and Lake Lanier are pushing drinking water suppliers toward extraordinary measures to keep metro Atlanta’s drinking water flowing and fit to drink.

In September, Cobb County officials dispatched divers to the bottom of the drinking water intake tower on Lake Allatoona. The officials needed to know if the fourth and lowest intake gate, unused since the tower was built in the mid-1960s, still functioned 40 years later.

They won’t know until the U.S. Corps of Army Engineers lets them dredge away the muck and sediment that’s blocking the lower gate.

Cobb officials have another contingency plan: running temporary pipes to a deeper part of the lake about a mile away.

“We have another month to two months to decide if we need to take that step,” said Glenn Page, general manager of the Cobb County-Marietta Water Authority.

The drought is challenging the ability of some treatment plants to draw water, as levels dip close to intake gates, and its myriad consequences are driving up the amount of chemical manipulation needed to make the water potable.

The additional measures don’t come cheap. The Cobb County-Marietta Water Authority, supplying drinking water to most of Atlanta’s northwestern suburbs, spent an additional $500,000 on chemicals this summer.

They estimate it will cost $600,000 to run temporary pipes to deeper water in Lake Allatoona, should that be necessary, plus monthly operating expenses of $250,000.

Last week, Cumming water officials in Forsyth County began dredging around their intake point on Lake Lanier to access deeper water.

The two- to four-week project will cost about $1 million, officials say.

Besides creating worries about sufficient quantity, the low water levels have complicated the purification process.

Water treatment managers have been coping with swings in water quality, requiring different strategies to eliminate odors, make the water clear and ensure that it’s safe to drink.

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