Uncertainty about the gravity of Oslo's contaminated water supply persists, but authorities insist that residents keep boiling tap water until the source of the apparently minor parasite outbreak is found.
Truls Krogh, head of water hygiene at the Norwegian Institute of Public Health (NIPH) said that water should be boiled until the source of Giardia and cryptosporidium parasites are found, and that this could take weeks.
This applies to about 457,000 Oslo residents served by the Oset water treatment plant.
"It will probably take a few weeks to determine if the situation is serious or not, then it will take another few weeks to clear up, if the situation is serious," Krogh said.
Krogh said that even though the parasite level is not likely to be anywhere near the outbreak in Bergen in 2004 that sickened at least 6,000 residents, authorities have decided to urge boiling.
Krogh has long had the condition of the capital's water pipes as a concern. The network from before 1970 is so poor that contaminated water leaks into the potable supply in several places, he told Aftenposten in January this year.
From early 2008 a new purification system at the Oset plant, which treats water from Lake Maridal and services about 80 percent of Oslo, should provide full protection against the types of parasite now found in recent samples.
According to an NIPH survey, 1.5 million Norwegians get water that can contain such parasites and 60 percent of Norway's waterworks do not meet purification standards.
Bergen's medical director for contagion protection, Øystein Søbstad advises the boiling of water for three minutes, and said that dishwashers are not a risk.
"The water in dishwashers usually is around 55-60C, which is not enough by itself, but modern detergents kill off parasites," Søbstad told newspaper Dagbladet's web site.
Aftenposten English Web DeskJonathan Tisdall/NTB
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