Sewage effluents, discharged into freshwater, estuarial and coastal waters present a risk to the user of those waters, should they contain viable (oo)cysts. The densities of (oo)cysts in inland waters receiving sewage effluent can be significantly greater than in those that do not receive such discharges (e.g. Parker, 1993; Medema and Schijven, 2001). During periods of prolonged or high rainfall, the volumetric design capacity in the sewerage network or at the sewage treatment works may be exceeded. in such circumstances, excess sewage is pumped straight to the receiving watercourse having undergone minimal (i.e. preliminary) treatment only, either at the sewage treatment works or within a combined sewer overflow (CSO) system. Gibson III et al. (1998b) found up to 40 000 oocysts/100 l and up to 283 000 cysts/100 l in effluent discharged from CSOs.Effluent irrigation and crop contamination.Although reuse of sewage effluent for crop irrigation is commonplace in arid regions of the world, few studies have assessed levels of protozoan contamination on irrigated crops such as fruit and vegetables, which are consumed raw. Field trials undertaken in Morocco revealed the presence of Giardia on coriander (254 cysts/kg), mint (96 cysts/kg), carrots (155 cysts/kg) and radish (59.1 cysts/kg) on crops irrigated with raw wastewater. Potatoes taken from a field irrigated with raw wastewater contained 5.1 cysts/kg (Amahmid et al., 1999). Earlier Mexican studies revealed the presence of Giardia cysts and other protozoan parasites on various fruit and vegetables irrigated with raw wastewater (Kowal and Pahren, 1982; Felix et al., 1996). A Costa Rican study (Monge and Chincilla, 1996) found that, of eight different fresh vegetables, commonly consumed raw, coriander roots and leaves, lettuce, radish, tomato, cucumber and carrot were contaminated with Cryptosporidium oocysts. Giardia was detected on coriander (cilantro) leaves and roots (Monge and Arais, 1996). Samples from vegetables collected at several small markets in a periurban slum in Peru harboured Cryptosporidium oocysts (Ortega et al., 1997). Of the vegetables examined, 14.5% contained C. parvum oocysts suggesting that washing vegetables does not completely remove Cryptosporidium oocysts. Such studies indicate the potential for fruit and vegetables to become contaminated and subsequently act as vehicles for the transmission of foodborne protozoan disease. A survey of lettuce and beetroot sold in a number of Chilean markets (Franjola and Guttierez, 1984) revealed the presence of Iodamoeba (Pseudolimax) butschlii and Entamoeba coli, indicative of faecal contamination (probably untreated wastewater used for irrigation). For vegetables and fruit that are eaten raw, the presence of infectious pathogens presents an unacceptable risk to the consumer.