"The DHB and relevant district councils are also informed of any results showing elevated bacterial levels within 24 hours and it's then their responsibility to take any further action required," NRC chairman Bill Shepherd said.
That action can include further site investigations to establish the source of contamination, public warnings not to swim or gather shellfish or putting up warning signs.
The summer testing regime resumed last Monday and will run until February 21.
Mr Shepherd said people can cut down any risk of infection by staying out of the water for two or three days after heavy rain which could carry run-off from land or where there are warning signs. They should avoid swimming where water has scum on the surface, is discoloured or smells.
Water quality concerns can be reported to the 24/7 Environmental Hotline on (0800) 504 639.