More than 400,000 Sydney residents received the all-clear yesterday to drink tap water but the NSW Government has admitted it may never know what caused the city's contaminated water crisis. Autopsies on two dead foxes from the upper canal had not shown levels of either giardia or cryptosporidium, a spokesman for Sydney Water, Mr Colin Judge, said. The Minister for Urban Affairs and Planning, Mr Knowles, said residents of 31 suburbs in southern and central-western Sydney could now drink water without boiling it but he could not confirm when the rest of the city's water supply would be safe to drink.