The tank at the Santa Teresa plant holds five-thousand gallons of ammonia that would normally be used in the water treatment process.
Hazardous response teams that responded found 250 gallons of ammonia did leak out of the tank and into an outer containment area, built around the tank. None of the ammonia escaped that secondary holding unit.
San Jose police didn't want to take any chances and went door-to-door telling nearby residents to stay inside. The warning applied to residents of Graystone Lane at Via Santa Teresa, Rosalind Lane; Skuse Court and Carriage Hill Drive.
"Inhaling large amounts of ammonia and having exposure can cause medical problems to get worse, it can cause other types of problems like difficulty breathing", said San Jose Fire Captain Steve Forman.
"Any time E.O.C. is in operation, I am concerned. Normally it's for flood calls or other emergencies, but occasionally we have activations from the water treatment plant. Our safety protocols have served us well," Gerry Uenaka from the Santa Clara Valley Water District said.
The warning to stay inside with doors and windows shut was lifted Saturday afternoon once crews were certain that no more ammonia was escaping from the tank.
Water district officials say there was never any exposure to drinking water since the plant is under construction and water is currently not treated there.