Boil water notices will remain in force throughout Queenstown, until the council can prove it's filtering protozoa, or parasites, out of the town's supply.
Drinking water for around 45,000 people is drawn from Lake Wakatipu.
National rules require protozoa barriers - Queenstown's Two Mile water treatment plant doesn't have one.
The Kelvin Heights water treatment plant does, but there are doubts about whether it's working.
Taumata Arowai, issued Queenstown's Council with a compliance notice yesterday - and the council has a deadline of 5 o'clock Thursday to respond.
Steve Taylor from Taumata Arowai the national water regulator spoke to Ingrid Hipkiss.