The invention relates to the use of water originating from the washing of lupines, with said water being retained. The water is filtered using cellulose filters and the resulting product is stored in containers. Next a bactericidal antiseptic, such as sodium benzoate or benzoic acid, is added. The water is then concentrated by means of reduced-pressure evaporation using a rotary evaporator at ambient temperature and, subsequently, packed in containers suitable for transport and use. The invention can be used for the production of environmentally friendly agricultural insecticides.
