Bath baby mum's guilt 'very raw' court told

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The actions of a mother whose son drowned when she left him alone in a bath to make a phone call were a major departure of care expected, a court was told today.

This morning, Crown prosecutor Sally Carter told the jury hearing the manslaughter case in the High Court at Wellington the 13-month-old boy drowned because of the actions taken by his mother.

"There was a major departure by [the mother] of the standard of care that was expected."

The child could not walk and could not speak enough words to call out for help, she said.

She noted evidence by two Plunket workers who said babies and toddlers settle into a state of relaxation when they go underwater, like they are in utero.

"They die quickly and quietly in 5cm of water."

The mother had never before left him alone in the bath before, so she must have known the risks, Ms Carter said.

She did not just leave her child in the bath alone, she purposefully went into the kitchen to make two phone calls and did not come back to the bathroom, even though it was a cordless phone, because she would not be able to hear the conversation.

She was away in total for seven minutes and 56 seconds.

"It's not a short period of time."

The woman, who has name suppression, was charged after her son drowned when he was left alone in a bath for nearly eight minutes.

He was found lying face down in 18cm to 19cm of water by his mother, who said she had been distracted by speaking on the phone to her mother.

Defence lawyer Noel Sainsbury told the court this was a case about whether the community marked a mistake with a conviction for manslaughter.

"There are things that happen that are terrible and tragic but we don't criminalise (people), we deal with them in different ways."

His client bore the burden of her actions, he said.

"The sense of guilt and responsibility is very intense and it's very raw."

It was not common knowledge about babies' reactions when they fall under water, "so when [the mother] said she didn't know, that makes sense", Mr Sainsbury said.

There were many cases where parents became distracted and their children seriously or fatally injured themselves.

"Do we charge them all with manslaughter? We all make mistakes, we are not machines," he said.

"We do not criminalise every mistake and it would be a travesty to criminalise this one."

The jury retired after the closing statements by the lawyers.

The trial in front of Justice Simon France in Wellington started on Tuesday.