A drinking water quality crisis occurred in Sydney, Australia, from July through September 1998. High concentrations of Cryptosporidium oocysts and Giardia cysts were repeatedly observed in water samples collected in the distribution system, although no increase in waterborne disease was detected. The reported concentrations of both cysts and oocysts ranged from nondetects to thousands of parasites per 100 L of finished water. Based on these monitoring data, three boil-water advisories were issued over a nine-week period. A formal government inquiry was ordered to investigate the cause of the contamination. The author visited the facilities involved and found that the laboratory providing the monitoring data had significant quality assurance and quality control problems, rendering the protozoan data suspect. Furthermore, data from other laboratories indicated the original reports were in error. In the author's opinion, reliance on poor-quality monitoring data created a water quality crisis when, in fact, no water quality problems or threats to public health existed. Includes 28 references, tables.