Maps on the Otago Regional Council website show the treatment plant is next to the former Cherry Farm landfill.
Its contamination status is listed as "not investigated".
The plant is close to Hawksbury which was the location of Cherry Farm Psychiatric Hospital until it closed in 1992.
Asked about the former landfill a Dunedin City Council spokesman said historic landfills in the area had been part of investigation into the lead contamination along with a number of potential other sources.
"This will be covered as part of the update at tonight’s meeting."
It comes as the communities of Waikouaiti, Hawksbury Village and Karitane are still waiting for answers five weeks after the council revealed it had known about the contaminated drinking water for six months.
Intermittent spikes in the level of lead, the highest almost 40 times the acceptable level, meant a no drink notice was issued on 2 February.
It remained in effect and could be so for months.
Unsafe levels of heavy metal were detected in some residents' blood, including children.
Waikouaiti resident Barbara Lawrence said she was among them.
"My blood came back high and they've given me a lovely little letter saying that it's because I stripped a house in 2007," she said.
She was frustrated by the authorities' response, not only to her own results but the lead scare in general.
She would be attending tonight's meeting but did not hold out hope of getting the answers she wanted.
"I think they'll just come back with our results and just compare it to a result that they've apparently had in the North Island and say everything's A-OK," she said.
"It doesn't really give us the answers we need as to why it took so long to give the community the heads-up something was wrong."
Most of the East Otago area's about 1500 residents had taken up the offer of a free blood test.
Another resident, Doug Luscombe, said his results were somewhat more reassuring, as he was under the internationally recognised safe blood-lead level of 0.24 micromoles per litre, but he felt the council had ignored the community and its infrastructure until the lead was detected.
"It's been neglected for years," he said.
"It's time they got off their bums and did something with it. We haven't even got decent footpaths to walk on out here. The old people have got to walk on the road and that's dangerous.
"We pay good money out here and we get nothing for it - rubbish collection, that's all we get."
He would be at tonight's meeting and had a simple request for authorities.
"Answers - that's all we want. Answers, and that's not much to ask."
Allan Hall, who worked behind the bar at the Golden Fleece Hotel one day a week, said he had heard of some concerning blood test results.
"I know of one little fella - about nine months old - his is quite high and an elderly lady, hers is quite high. But they both live in very old houses, so they've probably got lead in the pipes and paintwork."
Waikouaiti mother-of-two, Kate Mossman, said she the revelation of the lead contamination had caused a lot of anxiety for parents, and anger when they discovered the council had known about the issue for six months.
"It would've been nice to know and then from there we could've either thought, 'right, this is fine, we'll just roll with it' or say 'right, we'll do something about it and get our own water in'.
"We didn't have the choice to make our own decisions initially which is the worst part about it."
Her children, who were four and almost one, had grown up on the local water supply, but the whole family's blood test result showed nothing of concern.
A full house is predicted for the meeting at the East Otago Events Centre at 7pm tonight.
The Southern DHB will report back on the results and analysis of the blood tests carried out since the contamination was revealed, and the Dunedin City Council will also update the community on the investigations into the cause.
RNZ and ODT
