Tina Marie Alberson did not react as her sentence was announced. She was convicted last week of reckless injury to a child, a second-degree felony, in the July 2011 death of Jonathan James.
Jonathan’s mother, Krista Bishop, and other relatives said they were pleased with the verdict.
“We got what we needed,” Ms Bishop told reporters outside the court.
Police had thought Jonathan’s death was heat-related until the medical examiner’s report indicated otherwise.
Alberson, who testified in her own defence, told jurors that she limited Jonathan’s water intake a few times as punishment for misbehaving, and that she saw him drinking water when he wasn’t in “time-out.”
She said she saw no sign that he was in medical distress.
The boy’s twin brother Joseph James, now 12, testified that Jonathan repeatedly asked for water and pretended to use the bathroom so that he could sneak a drink from the faucet before their stepmother ordered him out. Joseph James told jurors he was concerned for his brother’s health but was too afraid of Alberson to do anything.