SMITHFIELD — Smithfield's water system is contaminated with potentially deadly E. Coli bacteria, according to test results released Wednesday afternoon, prompting town officials to order residents and businesses to boil water before using it.

Town officials used a reverse 9-1-1 system to broadcast an order that could be lifted as early as this afternoon if additional tests show the bacteria are gone.

Smithfield Utilities Director Earl Botkin said the contamination has been isolated to a home in the Longview Drive area of West Smithfield. Other testing sites are coming up clear, he said, but state regulations require the mandatory boil-water order.

The announcement Wednesday was a stronger warning than the voluntary advisory issued Tuesday afternoon, when testing showed only the possibility of contamination.

Botkin said crews from the N.C. Department of Environment and Natural Resources' Public Water Supply Section will be in Smithfield today to investigate the problem. They'll also install a backflow device designed to keep water from the contamination site from getting into the rest of the system.

"It's possible that some contaminants have gotten in the spigot [outside the house]," Botkin said, citing pet waste as a potential cause. "It's probably something that small."

E. coli can cause diarrhea, cramps, nausea, headaches and other symptoms; people with weak immune systems are at a higher risk. Botkin said the town hasn't received reports of anyone getting sick from the town's water supply.

Since Tuesday's advisory, restaurants and other businesses have been taking extra precautions, and bottled water has been flying off shelves at Smithfield's three grocery stores. At Food Lion, produce that normally gets watered is not being sold.

Smithfield's advisory does not apply to people outside the town limits who get their water from Johnston County's water plant. But on Monday, county officials, citing increased demand, asked its customers to conserve water. Specifically, the county is asking homeowners not to water lawns and shrubs, wash cars or test fire systems.

Those voluntary restrictions apply to rural residents and to water users in the towns of Clayton, Four Oaks, Princeton and Kenly. Also, they apply to customers of private utilities Aqua NC and Utilities Inc.

colin.campbell@newsobserver.com or 919-836-5768