The present invention relates to a method for recycling waste water from a stainless steel slag treatment process wherein stainless steel slag is brought into contact with water, in particular to neutralize the free lime contained therein, thereby producing said waste water. This waste water contains heavy metals, including at least chromium, and has a pH higher than or equal to 11. In accordance with the invention, it is used as production water for manufacturing mortar and/or concrete. In this way, the heavy metals, which are dissolved in the waste water and thus readily available, become bound in the newly formed cement phases so that they are prevented from leaching. Moreover, it has been found that the workability of the fresh mortar or concrete and also the quality of the final mortar or concrete materials is not negatively affected by the use of this alkaline waste water and that an accelerated setting could be achieved during the first hours.