The origins of the drought are not hard to identify. Combine the following and you have a recipe for a water shortage that could eclipse anything the Triangle has seen before:

NO RAIN. Rainfall is about 9 inches below normal for the year at Raleigh-Durham International Airport, and even less has fallen at some places in the Triangle. RDU received .91 inches of rain in August and 2.2 inches in September, the peak of the tropical storm season.

DESERT AIR. Tom Fransen, with the state's Division of Water Resources, said the Triangle did not experience much humidity over the summer. "We were more like the desert southwest," Fransen said. The lack of humidity increased the rate of evaporation on lakes, causing reservoirs to draw down more quickly.

BROILING AUGUST. This August was the hottest and second-driest month since at least 1944, when the area's record-keeping began at RDU. The temperature topped 90 degrees every day that month but one, and it exceeded 100 degrees six times. The Triangle tied or set record high temperatures 10 times, including only the third 105-degree reading in history. "August really clobbered us," said Mike Moneypenny, a hydrologist with the National Weather Service in Raleigh.

GEOGRAPHY. Unlike many other large metropolitan areas, the Triangle does not have a major river running through it, which means it draws water from smaller watersheds. That makes it more susceptible to drought.

RAPID GROWTH. The Triangle continues to draw residents and consume more water. In three decades or so, Raleigh's population is projected to reach 1 million. And hundreds of thousands more water customers will draw on the system in the six towns that Raleigh serves: Garner, Knightdale, Rolesville, Wake Forest, Wendell and Zebulon. By 2040, according to the city's estimate, Raleigh's maximum summer water demand will exceed its supply, even with an additional treatment plant and a new reservoir on the Little River.