Water/sediment quality guideline values are used as a general tool to help ensure that certain physical and chemical stressors in waterways do not exceed harmful levels.
We can define a guideline value as a measurable quantity (threshold) or condition of an indicator for a specific community value below or above which we consider to be a low risk of unacceptable effects occurring.
Site-specific guideline values
Ideally, you should use guideline values that are relevant to your to local conditions or situation. We call these ‘site-specific guideline values’.
relevant local authorities in your jurisdiction who might have developed site-specific guideline values.
We provide guidance in the Water Quality Guidelines on methods for deriving site-specific guideline values for protecting surface water aquatic ecosystems, which focus on the use of biological field-effects data, laboratory-effects data, reference-site data and the use of multiple lines of evidence.
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Default guideline values
If site-specific guideline values are not available, or have been agreed as being unnecessary, we provide or give directions to default guideline values (DGVs) for a range of stressors relevant to different community values, such as aquatic ecosystems, human health and primary industries.
DGVs represent a useful starting point for assessing water quality, and are recommended for generic applications in the absence of more relevant guideline values. DGVs may not be representative of your local conditions or situation but they can, to some extent, be tailored to make them more relevant to local conditions.
We provide DGVs for surface water aquatic ecosystem protection and primary industries, and direct you to DGVs for human health (e.g. drinking water, recreation and aesthetics).
DGVs for groundwater ecosystems have not been developed. In the absence of these, DGVs for surface water could be applied. However, first consider and possibly seek advice on their applicability.
We do not provide DGVs for cultural and spiritual values but these values are considered when setting water/sediment quality objectives (at Step 5 of the
Water Quality Management Framework).
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Guideline values should not be the only tool by which water quality is assessed.
You should use guideline values in conjunction with other lines of evidence in a
weight-of-evidence process to assess and manage water quality. This process will help you to assess water/sediment quality by looking at multiple indicators across lines of evidence for pressures, stressors and ecosystem receptors.
Guideline values for physical and chemical (PC) stressors and toxicants fall within the stressor lines of evidence.
Guideline values for New Zealand users
National Policy Statement for Freshwater Management (NPS-FM) resulted in the development of the National Objectives Framework (NOF). The NOF provides an approach to establish freshwater objectives for 2 compulsory national values (ecosystem and human health), and any other values, which are nationally consistent and recognise regional and local circumstances. It also includes national bottom lines for some measures of ecosystem health and human health.
No council in New Zealand can set a freshwater objective below a national bottom line, and water quality cannot be allowed to degrade across a region.
Users of the Water Quality Guidelines should be aware that regional councils and communities in New Zealand use these national bottom lines to set objectives, so regional plans may include specific reference to water quality measures.