This document provides guidelines for the evaluation of the fertilizer value of treated wastewater (TWW) at different treatment levels, for an effective fertilization of crops irrigated with TWW. This document covers:

—     evaluation of the nutrient quantities provided by TWW and the synchronization between crop needs and the nutrients applied with TWW;

—     availability of nutrients to crops irrigated with TWW;

—     monitoring nutrients in water, soil and crops irrigated with TWW;

—     matching between TWW quality and fertilizer properties.

Risk assessment and risk management for the safe use of TWW in irrigation projects are addressed in ISO 20426^[1] and ISO 16075-2^[2].