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New Zealand's rates of cryptosporidium infections are twice as high as Australia's, three times the UK's, and 10 times higher than the US.
And a leading researcher on parasites says there is much more we can do to help keep people, and animals, safe and healthy.
The national water authority Taumata Arowai has served Queenstown Lakes District Council with a compliance notice because its Two Mile water treatment plant does not have a protozoa barrier, which would prevent parasites entering the supply.
As a result the district's boil water notice will stay in place until such a barrier is installed - and the rest of the network is proven safe.
University of Otago parasitologist Bruce Russell spoke to Corin Dann.