Hawke's Bay aquifer systems are generally suitable for drinking water supply, according to a five-year groundwater quality report.
More than 5000 people fell ill last month after drinking water from the Havelock North town supply, which was contaminated with camplyobacter.
But the Hawke's Bay Regional Council report found 78 percent of the 40 monitoring sites around the region complied with the maximum acceptable values for drinking water.
The report said nitrate levels were typically low and all were better than drinking water standards.
It said just over 17 percent of Hawke's Bay sites had increasing nitrate-nitrogen levels, with the largest proportion being in the Ruataniwha aquifer system.
In the past five years, 88 percent of monitored sites were more than 90 percent compliant with E coli indicator levels.
The Regional Council said it had invested more than $7 million in the past five years, undertaking investigations and monitoring groundwater.