A method to reduce the amount of waste, in a process involving vaporization in an evaporator apparatus (1-6, V1-V6), of a water solution containing environmentally hazardous substances, wherein - a considerable amount of the water content of said water solution is vaporized by heating in at least one reusable vaporization chamber in a first vaporization process; - the water content of said water solution being vaporized into vapor, which is released, possibly after condensation into water, to an ambient system; - the vaporization process is stopped at a certain time at which the remaining water solution is removed from said at least one reusable vaporization chamber for further processing; - said certain time is adjusted so that the water content in said at least one reusable vaporization chamber is reduced, in said first vaporization process, by 30% to 95%, and the remaining water content is 70% to 5% of the initial water content, the remaining water content causing only minor deposits in said at least one vaporization chamber; - said remaining water solution, at said certain time, is transferred from said at least one reusable vaporization chamber into at least one separate waste isolating container; - whereupon said remaining water solution in said at least one waste isolating container is subjected to at least one further water-reducing process by heating, where the water content in said at least one waste container is further reduced by 10% to 100%; - the combined water-reduction in said first and further water-reducing processes being such as to leave a final water content in said at least one waste container of 10% to 0% of the initial water content of said water solution containing environmentally hazardous substances; - the remaining waste in said at least one waste isolating container, including said environmentally hazardous substances, is left in said at least one waste isolating container for handling as waste; - when the waste has reached a specified level in the at least one waste isolating container, the at least one waste isolating container is taken away and replaced; and - the at least one waste container containing the waste is subjected to a destructive treatment, such as incineration. - a considerable amount of the water content of said water solution is vaporized by heating in at least one reusable vaporization chamber in a first vaporization process; - the water content of said water solution being vaporized into vapor, which is released, possibly after condensation into water, to an ambient system; - the vaporization process is stopped at a certain time at which the remaining water solution is removed from said at least one reusable vaporization chamber for further processing; - said certain time is adjusted so that the water content in said at least one reusable vaporization chamber is reduced, in said first vaporization process, by 30% to 95%, and the remaining water content is 70% to 5% of the initial water content, the remaining water content causing only minor deposits in said at least one vaporization chamber; - said remaining water solution, at said certain time, is transferred from said at least one reusable vaporization chamber into at least one separate waste isolating container; - whereupon said remaining water solution in said at least one waste isolating container is subjected to at least one further water-reducing process by heating, where the water content in said at least one waste container is further reduced by 10% to 100%; - the combined water-reduction in said first and further water-reducing processes being such as to leave a final water content in said at least one waste container of 10% to 0% of the initial water content of said water solution containing environmentally hazardous substances; - the remaining waste in said at least one waste isolating container, including said environmentally hazardous substances, is left in said at least one waste isolating container for handling as waste; - when the waste has reached a specified level in the at least one waste isolating container, the at least one waste isolating container is taken away and replaced; and - the at least one waste container containing the waste is subjected to a destructive treatment, such as incineration.