However, she has criticised Environment Southland's Water and Land plan which aims to improve freshwater quality.
Stantec New Zealand principal environment scientist Sue Bennett gave evidence yesterday at Environment Court hearings of the proposed plan.
The hearing, which started last week, has 19 appellants.
Mrs Bennett was asked by the Invercargill, Gore and Southland District Councils to speak about the effects of stormwater and wastewater schemes.
She challenged part of the document which stated ''there is no reduction in the overall quality of freshwater, and water in estuaries and coastal lagoons'' by maintaining and improving the quality in water bodies.
She told the courtany discharge of waste water or stormwater, ''no matter how well treated'', would contain contaminants which would have cumulative effects on human health.
She believed water quality could not be simultaneously maintained and improved in the same location.
She said the wording of the objective could create confusion.
''In scientific terms, maintenance of water quality would be keeping it the same. Improvement would be a decrease in the levels of contaminants of concern within the water. Therefore, it can be one or the other, not both.''
Although she recognised the discharges from municipal wastewater schemes could affect bodies of water, Mrs Bennett believed it was not the only factor.
She said there were ''many options available'' to upgrade the quality of the discharge but none would result in complete removal of contaminants from storm water.
In her evidence, she also stated that increasing levels of treatment would increase the costs of the services.
Nga Runanga counsel James Winchester asked her about the councils' request to ''cut them a bit of slack'' in respect of the objectives and policies regarding to the discharge of storm and waste water.
She believed councils were not asking ''to be treated different'', but the plan should recognise the difficulty of the request.
Mrs Bennett believed this would mean that for every discharge, the council would need a consent or for the discharge to be considered either ''a discretionary or a non-complying activity''.
Mr Winchester also challenged the evidence from Invercargill City Council drainage and solid waste manager Malcolm Loan, who said the council managed stormwater and drainage networks from more than 20,000 properties and this was essential for the health and wellbeing of the community.
He said network discharges were managed in accordance with the consents and council was concerned ''to ensure that the objective of the proposed water and land plan do adequately provide for this infrastructure to be consent operated, maintained and upgraded over time''.
Mr Winchester said he was not questioning the importance of the council job but believed the council should ''play a part of the solution'' on the problem.
The hearing continues until next Tuesday.
