The 32-year old from Fullerton admitted that he ejaculated into an "attractive" co-worker's water bottle because "her lips had touched it," but told detectives he never thought she would drink it.
He faced a maximum sentence of one year in jail and sex offender registration.
He was charged in February with six misdemeanor counts of releasing an offensive material in a public place and assault, with sentencing allegations for committing a crime for sexual gratification.
Lallana's attorney, Eduardo Madrid, argued against the charged of misdemeanor assault and battery.
"There was no application of force," Madrid contended. "It doesn't make any sense. How could there be an assault? (The co-worker) wasn't even there."
The incident happened on Jan. 14, 2010, while both employees were working at the mortgage company, according to the Orange County district attorney's office.
Investigators say Lallana entered the victim's office and deposited his semen into a water bottle that was on his co-worker's desk.
The defendant is accused of leaving the semen-filled water bottle on the victim's desk, which she drank when she returned to her office.
The victim, who was unaware of the bottle's contents, drank the contaminated water. She threw it away after feeling sick, investigators say.
Three months later, the victim and six other employees, including the defendant, were transferred to the Northwestern Mutual Mortgage Company's Orange branch. That's where a second incident occurred, according to officials.
On April 9, 2010, Lallana is accused of assaulting the same victim by depositing his ejaculate into another water bottle that the victim left on her desk. The victim took a sip from the bottle, then felt sick. She decided to send the specimen to a private lab to be tested.
The lab contacted her and told her the water bottle contained semen, police said.
The victim then notified the Orange Police Department .
DNA tests confirmed the semen belonged to Lallana.