Sheep from paddocks near two Havelock North bores are being pinpointed as the probable cause of contamination leading to last year's mass gastro outbreak in the area.
More than 5000 people fell sick and one person died following the contamination in August last year.
The Government Inquiry into Havelock North Drinking Water began in the Hastings District Court today.
Hastings District Council Water Services Manager Brett Chapman is the first to give evidence in front of a packed courtroom.
Members of the public, officials and district mayor Lawrence Yule are all present.
He pointed at a number of key points on a map around bores on Brookvale Rd, where the contamination came from.
Under questioning, Mr Chapman admitted sheep from one of the paddocks surrounding those bores is the "probable cause" of contamination.
But it's still not known just how that contamination got into the water supply.
He was then asked by prosecuting counsel Nathan Gedye about the history of a Hawke's Bay Regional Council test bore about 200 metres from those bores.
That bore was found to have numerous e.coli readings from June 2008 until December 2015.
Mr Chapman admitted he wasn't aware of those readings until district authorities asked the regional council about readings following a well-publicised e.coli finding in September 2015.
The hearing is set to last for up to three weeks, with a report due before Attorney-General Chris Finlayson in March.
Mr Chapman also admitted that following last year’s outbreak, authorities now have a better understanding of how things in the surrounding area may have an effect on the bores and aquifer.
The council will now change their water safety plans for the area.
Havelock North residents remain connected to the Hastings water supply.