The use of wastewater for crop irrigation is becoming increasingly common, especially in arid and semi-arid areas. Crop yields are higher as the wastewater contains not only water for crop growth, but also plant nutrients (mainly nitrogen and phosphorus). However, there is the risk that wastewater irrigation may facilitate the transmission of excreta-related diseases. This laboratory manual describes procedures for the examination of treated wastewater samples to determine whether or not they comply with the guideline values publicated by the WHO. The procedures described have been selected because they are simple and require only the minimum of equipment; they can be readily carried out by laboratory technicians, even if they have no previous microbiological expertise. Section 2 describes a method of counting the number of intestinal nematode eggs in a wastewater sample, and section 3 describes two methods for counting the numbers of faecal coliform bacteria. These parasitological and bacteriological methods both focus on the analysis of samples at or near the quality guideline values given in Table 1, i.e. those containing about one intestinal nematode egg per litre and about 1000 faecal coliform bacteria per 100 ml, although they can be simply adapted to count much higher numbers. Finally, section 4 contains recommendations for routine monitoring programmes.