Two officers were injured when the boiling water was hurled at them in Abington, Northamptonshire, on Saturday night.
One suffered second-degree burns on the left side of his body, with the other treated for burns to his hand after they were rushed to Northampton General Hospital.
A teenage girl arrested at the scene appeared in court yesterday charged with GBH and assaulting an emergency worker.
She was released on unconditional bail to appear before Wellingborough Youth Court on November 17.
Home Secretary Priti Patel last night branded it a “disgusting attack on two of our incredible police officers”.
She added: “I struggle to comprehend how anyone could commit such an act.
“My thoughts are with these brave officers during this difficult time.”
Officers were called about midnight to an “extremely vulnerable young person”, Northants Police said.
Chief Constable Nick Adderley paid tribute to the injured men after the “appalling attack”.
“Once again, incidents such as these demonstrate the really challenging situations which our officers are left to confront on a daily basis.”
The injured officer had been on the force for just over two years before suffering “horrific injuries” in Saturday’s incident, said Sam Dobbs, chair of the Northamptonshire Police Federation.
He added: “While he comes to terms with his burns, we think also of the other officers who attended the scene and, using their excellent first-aid training, looked after the officer while arresting the suspect.”