From this afternoon, residents of of Karitane and Waikouaiti will be offered blood tests for chronic lead exposure after people in the East Otago towns were told not to drink the tap water because lead was detected in the reservoir.
One test in December that found lead levels were more than 40 times the maximum.
Southern District Health Board medical officer of health Dr Susan Jack said turn around time for the results from the lab were two days.
"If they do have elevated levels then they may have symptoms. Children may not have any symptoms at all, but they could be very non-specific symptoms such as a headache, muscle weakness, abdominal pain.
"What we are trying to to is see if people have been chronically exposed to lead and the best way to do that is blood levels, so that's what we have committed to do and are starting to do with the communities starting today."
"What we are trying to to is see if people have been chronically exposed to lead" - Dr Susan Jack
Chronic exposure meant repeated exposures, Jack said.
"We don't believe that is the case because the evidence to date from the testing is that it's just been intermittent spikes, however, because the testing only began six months ago, that's why we're going ahead [with testing]."
If it were just a one-off event, there was not likely to be any impact on blood lead levels, she said.
"We do expect because of other exposures that there will be low levels of lead in people's blood, however, what we are looking for is elevated levels.
"Everyone who has a blood test, we are also asking to fill out a questionnaire which goes through all those possible exposures so when we get the results we can make some sense of that."