Police said two of the woman's children had died of natural causes earlier. (Representational)

A 35-year-old woman in Rajasthan's Kota allegedly drowned her six-month-old son in a water tank, police said on Tuesday. The woman, identified as Deepika Gujjar, a resident of Saraswati Colony in Kota, claimed she woke up from deep sleep, drowned the child and then went back to sleep in the early hours on Sunday, police said.

She also told the police that she didn't know why she committed the alleged crime. She has been arrested under Section 302 of the Indian Penal Code.

According to police, she took the baby, Shiva, to the second floor of their three-storeyed house and drowned him in the water tank before going back to sleep on the first floor.

The incident came to light when her husband Sitaram Gujjar, who is a teacher, found the boy missing around 1.30 am.

The accused joined her husband Sitaram and mother-in-law Kelabai to find the child without mentioning the alleged crime to them, police said.

Her mother-in-law found the baby in the water tank.

Police said though the incident was reported on Sunday afternoon, the woman continued to mislead them till the next day. Senior police officer Harendra Singh said that she started crying during questioning and confessed to the crime.

Mr Singh said the woman "unknowingly" took the baby to the water tank and drowned him in it. He, however, added that the motive behind the crime was yet to be ascertained.

Police said they had zeroed in on the accused, her husband and mother-in-law as they were sleeping with the child at the time of the incident.

The Station House Officer added the woman had no history of any mental disorder, but they were probing this aspect as well.

Two of her children had died of natural causes earlier.