Water quality guidelines
For general information on water quality guidelines refer to the fact sheet Deriving local water quality guidelines.
Water quality guidelines are technically-derived numerical measures (e.g. concentrations) or descriptive statements to protect aquatic ecosystems and human water uses and values (e.g. irrigation, stock watering, recreation). They can be derived for a range of physico-chemical, biological and habitat indictors based on best-available science. In Queensland, water quality guidelines are developed under the frameworks outlined in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (Australian and New Zealand Environment and Conservation Council – ANZECC, 2000) and the Queensland Water Quality Guidelines. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality have been prepared as part of Australia’s National Water Quality Management Strategy (NWQMS).
The waterway uses and values (also called ‘environmental values—EVs’) recognised in the national guidelines include:
- aquatic ecosystems
- primary industries, (including irrigation, stock watering, aquaculture, human consumers of aquatic foods, general farm use)
- recreational use (swimming, boating, visual recreation)
- drinking water supply
- industrial water
- cultural and spiritual values.
Each of these EVs require its own specific set of guidelines because the acceptable guideline values to support one type of EV may not be acceptable to maintain another EV. For example, the guideline values for pesticides required to protect fish and other fauna are usually lower than those required for protection of irrigated crops. Another reason is that the indicators relevant to one EV may be different to those used for other EVs.
Guidelines for human use EVs are almost all expressed as a single value of an indicator that applies uniformly across Australia (e.g. salinity guidelines for crops in Queensland are the same as those in West Australia). Human use EV guidelines are also dominated by physico-chemical indicators. As a result, these guidelines are relatively simple in concept and application. Examples of human use water quality guidelines include are provided in the fact sheet Deriving local water quality guidelines.
Water quality guidelines for aquatic ecosystem protection are considerably more complex, because:
- aquatic ecosystem protection guidelines for some indicators (e.g. nutrients, chlorophyll-a, biological) need to be specific to different regions (e.g. Wet Tropics versus South East Queensland) because there are natural variations in their values
- within each region, aquatic ecosystem protection guidelines for some indicators (e.g. nutrients, chlorophyll-a, biological) need to be tailored to different water types (e.g. fresh waters, estuaries, coastal and marine waters, lakes and reservoirs) because they have naturally different values of these indicators. As there are different flora and fauna in these water types, guidelines for toxicant indicators may also have to be tailored (e.g. coral reefs may be more sensitive to some pesticides than inshore or freshwater flora and fauna)
- the ANZECC guidelines have specified three different levels of aquatic ecosystem protection (high ecological value, slightly to moderately disturbed, highly disturbed), for which different guideline values may need to be derived.
The need to develop aquatic ecosystem guidelines for more localised regions and water types is one of the main reasons why the Queensland Water Quality Guidelines were developed. These are aimed at developing and capturing regional and local data to a degree that is simply not possible in national guidelines.
Information on the process of deriving water quality guidelines is contained in the fact sheet Deriving local water quality guidelines.
The Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC, 2000) recommend two main approaches to developing guidelines:
Guidelines based on direct impact studies
This approach is best suited to the development of guidelines for physico-chemical indicators. It relies on development of a relationship between the indicator and the EV in question. Examples of this would include impacts of:
- salinity on crops
- blue-green algae on humans or stock
- toxicants or low dissolved oxygen on biota
- reduced light penetration on seagrass growth.
Based on known relationships, we can determine an acceptably safe level of the instream pressure indicator and use this as a guideline value. Developing guidelines using this approach requires a high level of technical expertise and resources. Therefore, this approach is usually confined to universities or other research organisations.
Guidelines based on a referential approach
For many aquatic ecosystem indicators, guidelines are developed using a referential approach. This approach is best suited to biological indicators (e.g. macroinvertebrate diversity) or to physico-chemical indicators (e.g. nutrients) where there are no simple direct-impact relationships.
Using a referential approach, guideline values for a particular indicator are determined by the condition of that indicator in a relatively undisturbed system. This becomes the reference condition. For example, dissolved oxygen guidelines would be based on typical dissolved oxygen values found in a relatively undisturbed system. Similarly, guidelines for biological indicators, such as macroinvertebrates, would be based on macroinvertebrate populations found in undisturbed systems.
The actual guideline value is calculated on the basis of maximum acceptable departure from reference condition. The default acceptable departure suggested in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (section 18.104.22.168) is that the guideline value be based on the 20th and/or 80th percentile (whichever is most appropriate for the indicator) of values at the reference site.
The referential approach can be used by regional groups. Provided that reference data is collected according to agreed protocols (adequate numbers of reference sites and data values, time periods of collection and quality assurance) then such groups can use their own monitoring data to develop local guidelines.
For more information refer to the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (pages 3.3–6 to 3.3–9) and the Queensland water quality guidelines.
Water quality guidelines and water quality objectives
Water quality guidelines are often confused with water quality objectives. While guideline values are commonly used as the basis for water quality objectives, conceptually the two are quite distinct, as outlined by the Australian and New Zealand guidelines for Fresh and Marine Water Quality:
‘A water quality guideline was defined above as a numerical concentration limit or descriptive statement recommended for the support and maintenance of a designated environmental value. Water quality objectives take this a step further. They are the specific water quality targets agreed between stakeholders, or set by local jurisdictions, that become the indicators of management performance.’
While guidelines are the technical basis of objectives, final water quality objectives take into account social and economic factors and are ultimately agreed to by all stakeholders. They also usually have some legislative standing whereas guidelines may not. In Queensland, documents containing EVs and the water quality objectives to support them are listed in schedule 1 of the Environmental Protection Policy for Water. These are available from the department’s web page at Environmental values - Environmental Protection (Water) Policy 2009. In areas where no water quality objectives are scheduled, the Queensland water quality guidelines apply as default objectives.
As with guidelines, the term ‘water quality objective’ has traditionally referred only to the physical and chemical characteristics of waters. In modern usage, water quality objectives can encompass a broader range of characteristics including flora and fauna, habitat, flow and physical condition.