A San Antonio grandmother has been sentenced to 18 years in prison in the 2005 drowning death of her 3-month-old granddaughter.

The San Antonio Express-News reported that because the Bexar County jury considered the water in the swimming pool a deadly weapon, Gabriella Sigler must serve half of the sentence before being eligible for parole.

Sigler, who was sentenced Thursday, pleaded guilty to injury to a child resulting in serious bodily injury.

She was watching the baby when authorities said she ignored her son's warnings and put Melody Sigler in the pool.

Defense witnesses testified Sigler was suffering from a manic episode caused by bipolar disorder.

Police said Sigler admitted to using drugs the night before and drinking wine the morning Melody died.