there is provided a process for the purification of ammonia or ammonium salt containing waste waters using alkali metal or alkaline earth metal hypochlorites comprising adjusting the waste water to an initial ph of 8 - 10 . 5 with an alkaline material and then treating the waste water with an alkali metal or alkaline earth metal hypochlorite in an amount practically equivalent to the ammonia or ammonium salt , in a given case while lowering the ph during the evolution of nitrogen by additional neutralization of this ph to about 6 - 8 whereupon only after the end of the evolution of nitrogen the ph of the waste water , if it deviates from 7 , is adjusted to the neutral region in known manner . the initial ph is preferably adjusted with the help of an alkali or alkaline earth hydroxide , most preferably it is adjusted to a ph of 8 - 9 with the help of a buffer salt .