Almost a third of Southland's groundwater bore samples failed to meet national drinking standards last year, Environment Southland (ES) report cards revealed last month.
The Groundwater Quality Report Card 2012/2013 shows bacteria levels did not meet drinking water standards in 27% of bores sampled - 69 out of 258 bores.
However, Environment Southland principal scientist Clint Rissmann said scientists deliberately targeted bores with poor water quality over the past 18 months.
''It is significantly higher this year because we have been trying to actively sample some of those poor quality bores to get a better idea of what is happening in the region.''
Two-thirds of the bores with poor quality had localised pollution, which meant the bacteria and nitrate contaminants getting into the water could be easily stemmed, he said.
Often the problem was self-installed wells or well heads, which were not properly fenced off which made it easy for contaminants to find the water. ''The good thing is, if it is a localised problem, we can change and improve it.''
The remaining bores were being contaminated with widespread pollution, which was harder to control, he said.
Half of bores sampled for nitrate over the 2012-13 financial year indicated a significant impact from land use activities. Ten percent of bores sampled exceeded national drinking water standard for nitrate of 11.3mg/L.
Dr Rissmann said while the general trend for nitrate concentration was showing deterioration across the region, bacteria contamination was improving. ''I do believe that there has been a bit of improvement overall in terms of bacteria levels, although it won't be shown in this year's results.''
Meanwhile, rivers and streams in lowland Southland areas had high levels of sediment nutrients and faecal bacteria, with many waterways above the Australia and New Zealand Environment Conservation Council (Anzecc) guidelines.
In particular, the Waimatuku, Waihopai, Mid Mataura, Waituna/Awarua, Makarewa, Lower Oreti, Lower Mataura, and Catlins zones had nutrient levels above the guidelines.
Environment Southland surface water scientist Roger Hodson said the levels of faecal coliforms in the waterways gave an indication of how much faecal contamination was in the river, and if it was suitable to drink, swim in or fish from. ''It's really important for the community to know about faecal contamination.
''A waterway can make you sick if it is contaminated. If you are going swimming, or put your head under the risks of contact with contaminated water are higher.
''Collecting food can also be a risk, especially if you are collecting watercress or shellfish.''
Mr Hodson said the levels of sediment nutrients and faecal bacteria had not changed dramatically in Southland waterways since last year. Areas which had a higher proportion of land use and agriculture had higher nitrate and phosphorus in the waterways, he said.
- by Leeana Tamati