Drinking Water – What’s in a Grade?
Our results aren‘t simply pulled out of the sky, they have been prepared using a set of formulas and scores that are applied from the indicator level all the way to the grade for a water supply. All of these steps and their application are based on best available science along with the expert knowledge and guidance of our science panel.
Drinking Water Grades
The drinking water reporting products use data provided by our Regional Council partners. Indicators, thresholds and normalising formula are used to determine grades and are covered in more detail below.
Sometimes there are no data available to assess an indicator or a water supply in a particular year. When this is the case a grey N icon is displayed.
Raw Water Source
Raw water is sourced from surfacewaters, like rivers or dams
Water is sourced from groundwaters
Drinking water reports have been prepared by applying a selection of Australian Drinking Water Guidelines (NHMRC, NRMMC 2011) to data provided by Councils and other suppliers of water to townships. The Australian Drinking Water Guidelines include two different categories of guideline values:
- “A health-related guideline value, which is the concentration or measure of a water quality characteristic that, based on present knowledge, does not result in any significant risk to the health of the consumer over a lifetime of consumption; and
- an aesthetic guideline value, which is the concentration or measure of a water quality characteristic that is associated with acceptability of water to the consumer; for example, appearance, taste and odour.” (NHMRC, NRMMC, 2011)
Raw water comes from natural sources such as creeks, rivers, dams and groundwater and has not yet been treated for use as drinkable water. Councils and other suppliers of water to townships process this raw water to make it more drinkable, potable or useful by purifying, clarifying, softening or deodorizing it. Treated water is then provided to the community as drinking water and for other uses.
As raw water is not usually intended as drinking water, poor scores for raw water do not suggest that drinking water is contaminated or of poor quality. Raw water grades are provided in the reporting products for interest as they provide some indication of the quality of water in the aquatic ecosystems from which they are drawn.
By comparison to the “Treated” grades they also demonstrate how effective modern water treatment processes are at treating water for human consumption. There may on occasions be issues with raw water that affect treatment processes, and conversely situations where raw water is of good quality and the costs of treatment are lower.
The Australian Drinking Water Guidelines recognise that occasionally there may be health or aesthetic related test results that fall outside the guidelines and that these results are not necessarily an immediate threat to health. The guidelines do not require a 100% result for all parameters in all cases.
The Partnership uses data provided by Councils to score drinking water against 22 indicators. Indicators were selected using the same criteria as for the EHI and those chosen for inclusion are both currently monitored and have an available guideline for drinking water quality.
How are Grades Awarded?
Grades are provided for both Health and Aesthetic guidelines when possible. Treated water results are only provided when the water has been treated and data are available for analysis. These data are averaged and graded using a similar approach to that taken in the Partnership’s Marine reporting, as follows:
Individual scores are given to each data point for each parameter/indicator based on a pass/fail approach
- Green thumbs up: Results are within health and aesthetic guidelines
- Orange thumbs up: Results exceed aesthetic guidelines
- Red thumbs down: Results exceed health guidelines
With the exception of electrical conductivity and pH which are described further below, each data point is given a score of 0 or 100 for each of health and aesthetics (based on the pass/fail mechanism). The scores are averaged to give an overall grade to the relevant site for each indicator, for both health and aesthetic characteristics
- A = 80 – 100. Excellent.
- B = 60 – 80. Good.
- C = 40 – 60. Fair.
- D = 20 – 40. Poor.
- E = 0 – 10. Fail.
- N = No data.
The 22 indicators are weighted evenly and averaged to give an overall site grade, A to E.
This process is carried out for both:
- Treated water
- Raw water
An example of the scoring method:
- Sulfate concentration (mg/L) at Rockhampton is measured monthly throughout 2010.
- Each measurement of sulfate is given a score of 0 (fail) or pass (100) based on each of the aesthetic (250 mg/L) and health (500 mg/L) guidelines for sulfate.
- All of the sulfate scores for the year are averaged for the Glenmore site to give both a health and an aesthetic grade for sulfate at Rockhampton in 2010 (A to E).
- The grades for each of the up to 22 indicators measured at Rockhampton during 2010 are averaged for Health and Aesthetics, using equal weightings in both cases, to provide overall site grades for Rockhampton (A to E).
- This process is carried out for both treated water and raw water readings from the Rockhampton site.
- Thus, Rockhampton effectively gets allocated four final grades: Health of treated water, Aesthetics of treated water, Health of raw water and Aesthetics of raw water.
Scoring electrical conductivity:
Individual data points are given a pass/fail (100/0) score for each of Health and Aesthetics. However for calculating a site grade for electrical conductivity, each data point is given a score on a sliding scale. For electrical conductivity this scale is as follows:
- Less than 940 µS/cm = 100
- Greater than 940 µS/cm but less than 1400 µS/cm = 66
- Greater than 1400 µS/cm but less than 1875 µS/cm = 33
- Greater than 1875 µS/cm = 0
The scores for each data point are then averaged to give a site grade of A to E on the scale described above.
Similar to electrical conductivity, individual pH data points are given a pass/fail (100/0) score for each of Health and Aesthetics. To calculate a site grade for pH, each data point is given a score on a sliding scale. For pH this scale is as follows:
- Greater than or equal to 6.5 and less than or equal to 8.5 = 100
- Greater than 4.5 and less than 6.5 = (pH reading2)/(6.52)
- Greater than 8.5 and less than 11 = (15 – pH reading)2)/(6.52)
- Less than or equal to 4.5 = 0
- Greater than or equal to 11 = 0
The scores for each data point are then averaged to give a site grade of A to E on the scale described above.
Indicators and Thresholds
Drinking water indicators and their health and aesthetic guidelines used in this reporting are sourced from the Australian Drinking Water Guidelines. Measures are in mg/L unless otherwise specified (Source: NHMRC, NRMMC, 2011).
|Indicator/Parameter||Health Guideline||Aesthetic Guideline||Comments|
|Aluminium||c||0.2||Guideline value based on post-flocculation problems; < 0.1 mg/L desirable. Lower levels needed for renal dialysis. No health-based guideline value can be established currently.|
|Chloride||c||250||From natural mineral salts, effluent contamination. High concentrations more common in groundwater and certain catchments.|
|Escherichia coli||0cfu/100 mL||Escherichia coli should not be detected in a minimum 100 mL sample of drinking water.|
|Colour||15 HU||An important aesthetic characteristic for customer acceptance. Treatment processes can be optimised to remove colour.|
|Copper||2||1||From corrosion of pipes/fittings by salt, low pH water. Taste threshold 3 mg/L. High concentrations colour water blue/green. >1 mg/L may stain fitings. >2 mg/L can cause ill effects in some people.|
|Cyanide||0.08||From industrial waste and some plants and bacteria.|
|Electrical conductivity*||940µS/cm**||Occurs naturally in water and may be elevated by some land uses.|
|Fluoride||1.5||Occurs naturally in some water from fluoride-containing rocks. Often added at up to 1 mg/L to protect against dental caries. >1.5 mg/L can cause dental fluorosis. >4 mg/L can cause skeletal fluorosis.|
|Iron||c||0.3||Occurs naturally in water, usually at <1 mg/L, but up to 100 mg/L in oxygen-depleted groundwater. Taste threshold 0.3 mg/L. High concentrations stain laundry and fittings. Iron bacteria cause blockages, taste/odour, corrosion.|
|Lead||0.01||Occurs in water via dissolution from natural sources or household plumbing containing lead (e.g. pipes, solder).|
|Manganese||0.5||0.1||Occurs naturally in water; low in surface water, higher in oxygen depleted water (e.g. groundwater at bottom of deep storages). >0.1 mg/L causes taste, staining. <0.05 mg/L desirable.|
|Nitrate||50||Occurs naturally. Increasing in some waters (particularly groundwater) from intensive farming and sewage effluent. Guideline value will protect bottle-fed infants under 3 months from methaemoglobinaemia. Adults and children over 3 months can safely drink water with up to 100 mg/L nitrate.|
|Nitrite||3||Rapidly oxidised to nitrate (see above).|
|Sodium||No value||180||Natural component of water. Guideline value is taste threshold.|
|Sulfate||500||250||Natural component of water, and may be added via treatment chemicals. Guideline value is taste threshold. >500 mg/L can have purgative effects.|
|Total dissolved solids||No value||600||Based on taste: <600 mg/L is regarded as good quality drinking water. 600-900 mg/L is regarded as fair quality 900-1200 mg/L is regarded as poor quality >1200 mg/L is regarded as unacceptable.|
|Total hardness||200||Expressed as a calcium carbonate equivalent. Hard water requires more soap than soft water to obtain a lather and can cause scale on hot water pipes and fittings. Caused primarily by the presence of calcium and magnesium ions, although other cations such as strontium, iron, manganese and barium can also contribute.|
|Trihalomethanes||0.25 e||By-product of chlorination and chloramination. Action to reduce trihalomethanes is encouraged, but must not compromise disinfection, as non-disinfected water poses significantly greater risk than trihalomethanes.|
|Turbidity||c||5 NTU||5 NTU is just noticeable in a glass. <0.2 NTU is the target for effective filtration of Cryptosporidium and Giardia. <1 NTU is the target for effective disinfection.|
|Zinc||c||3||Usually from corrosion of galvanised pipes/fittings and brasses. Natural concentrations generally <0.01 mg/L. Taste problems >3 mg/L.|
|pH*||c||pH 6.5-8.5||While extreme pH values (<4 and >11) may adversely affect health, there are insufficient data to set a health guideline value. <6.5 may be corrosive. >8 progressively decreases efficiency of chlorination. >8.5 may cause scale and taste problems. New concrete tanks and cement-mortar lined pipes can significantly increase pH and a value up to 9.2 may be tolerated provided monitoring indicates no deterioration in microbial quality.|
HU = Hazen units; NTU = nephelometric turbidity units
c – insufficient data to set a guideline value based on health considerations
e – the concentration of all chlorination byproducts can be minimised by removing naturally occurring organic matter from the source water, reducing the amount of chlorine added, or using an alternative disinfectant (which may produce other byproducts). Action to reduce trihalomethanes and other byproducts is encouraged, but must not compromise disinfection.
Note: All values are as ‘total’ unless otherwise stated.
Note: Routine monitoring for these compounds is not required unless there is potential for contamination of water supplies (e.g. accidental spillage).
* electrical conductivity and pH are scored using a pass/fail mechanisms as for other parameters, but are graded on a sliding scale
** the aesthetic guideline for electrical conductivity has recently been removed from the Australian Drinking Water Guidelines but was in place at the time of the reporting period (2011-12 and 2012-13). Values are now derived from total dissolved solids (TDS).