Water quality guidelines

Site specificity

National water quality guidelines are intended to be broadly applicable across the country. However, unique conditions in some places mean that the guidelines may be over- or under-protective in some areas.

For example, this might occur if there are species in an area that are more sensitive (or less sensitive) than the species that were studied when the guideline was developed. In other cases, natural background levels of a substance may exceed the guideline without any observed effect on locally adapted species. Additionally, the unique mix of substances and attributes of water at a given location may result in a substance being more toxic (or less toxic) than it was found to be under the range of conditions that were studied in setting the guideline.

Acute vs chronic guidelines

Acute guidelines are set based on the effects of short-term, transient exposures (e.g., abnormal discharges and spills) and generally present higher concentration levels.

Chronic guidelines, in contrast, are based on the effects of continuous, long-term exposure and have lower recommended concentration levels.

CCME and US EPA guidelines use slightly different approaches in defining and assessing acute vs chronic exposures.

• CCME Acute: These guidelines are created using data from short-term exposure periods (24-96 hours). The concentration levels specified are not intended to protect against adverse effects, but rather indicate the level where severe effects are likely to be observed.
• US EPA Acute: These guidelines refer to the highest 1-hour average concentration that should not result in unacceptable effects if it does not occur more than once every three years, on average.
• CCME Chronic: These guidelines identify maximum concentration levels (or ranges for attributes such as pH) that are intended to protect all forms of aquatic life, at all life stages, for indefinite exposure periods (≥7 day for fish and invertebrates, ≥24 hour for aquatic plants and algae).
• US EPA Chronic: These guidelines refer to the highest 4-day average concentration that should not result in unacceptable effects if it does not occur more than once every three years, on average.

Freshwater vs marine guidelines

Freshwater and marine environments have fundamental differences in water chemistry. For this reason, separate guidelines are set for these two different water body types. To date, guidelines have not been developed that are specific to the protection of estuarine species.

CCME provides the following definitions for each water body type:

• Freshwater: Total Dissolved Salt Content ≤ 1000 ppm (1 g/L or 1 ppt)
• Marine: Total Dissolved Salt Content > 5000 ppm (5 g/L or 5 ppt)

We have compiled a Water Quality Guideline Summary Spreadsheet that lists all CCME, ECCC and US EPA guidelines for the protection of aquatic life, their translation to DataStream characteristic names, corresponding equations (where applicable), and links to source/reference material for each guideline.

Calculated guidelines

The following table outlines all characteristics that use equations to determine their guidelines as well as the characteristic that these equations are dependent on. These calculated guidelines relate to freshwater guidelines only. To view the equations in their entirety, please see DataStream’s Water Quality Guideline Summary Spreadsheet.

Characteristics with calculated guidelines and their dependencies

Hardness calculations and conversions

Both US EPA and CCME guidelines contain equations that are hardness dependent. The hardness for these guidelines is expressed in ‘Total hardness’ with units of mg/l and speciation ‘as CaCO3’. ‘Hardness, Ca, Mg’ can also be used instead of ‘Total Hardness’ as they are synonymous.

When ‘Total hardness’, or ‘Hardness, Ca, Mg’ exists with either a different unit or speciation, the original value is multiplied by the corresponding conversion factor to obtain the standard units and speciation.

Hardness conversion table

If neither ‘Total hardness’ or ‘Hardness, Ca,Mg’ exists, ‘Total hardness’ can be calculated using the following equation and concentrations of ‘Magnesium’ (Mg2+) and ‘Calcium’ (Ca2+) in mg/l.

Total Hardness [CaCO3] = 2.497*[Ca2+] + 4.118*[Mg2+]

If neither ‘Total hardness’ or ‘Hardness, Ca,Mg’ exists, and both concentrations of ‘Magnesium’ (MG2+) and ‘Calcium’ (Ca2+) don’t exist, ‘Total hardness’ can be calculated using the following equations along with ‘Hardness, magnesium’ and ‘Hardness, calcium’ in mg/L.

Total Hardness [CaCO3] = ‘Hardness, magnesium’ + ‘Hardness, calcium

Finally, if none of the previous characteristics required are available, the ‘Total hardness’ can be calculated using the following equation and ‘Hardness, carbonate’ and ‘Hardness, non-carbonate’ in mg/L.

Total Hardness [CaCO3] = Hardness, carbonate + Hardness, non-carbonate