ACT State of the Environment 2007

Indicator: Drinking water quality

Summary

The primary challenge for drinking water in the ACT during the reporting period was low availability of water as a result of the prolonged drought. Despite this challenge, the quality of water at the tap remained high; a consistent feature of the ACT potable water supply.

What the results tell us about the ACT

During the reporting period, the major problems for drinking water in the ACT developed or become more apparent as a result of the drought. The significance of this drought has caused the landscape to respond in a variety of ways, the most obvious being low water yields from the catchments and the bushfire in January 2003.  As a result of the challenges the drought has presented, the ACT Government and community have focused on better water management techniques; some of which have created significant cultural change to the way water is managed and used in the ACT.

The main effect of the drought on the ACT has been reduced availability of drinking water. During the reporting period, inflow to the water supply reservoirs was approximately 38% of the average 187 GL per year (Figure 1). The low inflows, combined with high evaporation rates and high consumption, meant the storage capacity of water supply reservoirs fell to 31% in June 2007. The reduced water availability in the region caused the ACT Government the change several key water policies in an effort to secure the ACT's water supply.

As well as drinking water availability, soil erosion in the Cotter River catchment following the January 2003 bushfire saw temporary water quality problems for short periods during 2003 and 2004. During these times drinking water was sourced from the Googong Reservoir, a treated raw water source to the east of the ACT, thus ensuring no supply disruption to the ACT. However, in response to water quality problems in the Corin and Bendora reservoirs, the Mount Stromlo Water Treatment Plant was constructed to safeguard against future possible water quality problems and to provide the ACT with access to the water resources of the Cotter Dam and Murrumbidgee River.

Despite the enormous challenges the ACT faced during the reporting period, the drinking water quality at the tap continued to meet the requirement of the Australian Drinking Water Guidelines. An important addition to safeguarding the ACT's water supply is construction of the Mount Stromlo Water Treatment Plant. The Plant provides a management barrier to prevent interruption of the water supply by events such as the 2003 bushfire. While the catchment quickly returned to producing clean water, both prescribed and unplanned future fires have the potential to upset the catchment's ability to supply clean water to the ACT. The Mount Stromlo Water Treatment Plant now strengthens the multiple barrier approach to water quality management of water sourced from the Corin and Bendora catchments.

Figure 1 : Dam storage levels, 2003–07

Graph of the combined fullnes of all Canberra's water supply dams

Source: ACTEW AGL 2007 Drinking water sources diversified

The pressure of the drought on water availability in the ACT prompted the ACT Government, ActewAGL and the community to undertake a significant review of the availability of water supply sources. The Water Security program was initiated to explore availability options through expert and community consultation. Commissioning of the Mount Stromlo Water Treatment Plant created the opportunity for the ACT to use the Cotter Reservoir and Murrumbidgee River as water sources. Drinking water was sourced from the Cotter Reservoir in December 2004 after the Cotter pump station was recommissioned. Similarly, in May 2007 the Murrumbidgee River was used as a drinking water source for the first time since the 1960s.

Drawing water from the Murrumbidgee to supply drinking water for the ACT community provides a third source catchment of water in times of reduced inflow to the dams. Other options for securing the ACT's drinking water are discussed in Water use.

High quality drinking water in the ACT

The standard of drinking water remained high during the reporting period. Typically the Corin and Bendora reservoirs had good yield and high quality water and, under normal operating conditions, they would supply 90 to 95% of Canberra's water supply without filtration. The remaining component (summer peaks and during Bendora reservoir turnover) was supplied from the Googong reservoir on the Queanbeyan River. As a precautionary measure following the 2003 bushfire, Mount Stromlo Water Treatment Plant was constructed to manage poor water quality from Bendora dam as a result of the fire. The water quality from the Corin and Bendora dams has since returned to normal with little to no treatment necessary. The Mount Stromlo Water Treatment Plant is now used to manage water quality problems from the Cotter Dam and the Murrumbidgee River, when these sources are needed.

The microbiological quality of drinking water was reported to be of a high standard in each year of the reporting period. The percentage of total coliforms meeting the target was lowest in 2003–04 with 98.2% of samples taken (see Table 1) and highest in 2005–06 with a 100% success rate (see Table 3).

There was a noticeable improvement in samples of pH meeting the target in 2006–07 (see Table 4). This was achieved by the improved buffering capacity of water from the Mount Stromlo Water Treatment Plant (ActewAGL 2007).

Turbidity levels have noticeably improved since the water treatment plants were upgraded in 2004, although in 2006–07 the taking of larger quantities of water from the Googong Dam resulted in a slight increase in turbidity levels, as the Googong Water Treatment Plant has different treatment characteristics from that of the Mount Stromlo plant.

Table 1: Drinking water quality monitoring results, 2003–04
Parameter Target/Units No. of samples No. meeting target % meeting target Mean Min Max
pH 6.5–8.5 940 864 91.9 7.93 7.2 10.3
Alkalinity <200 as CaCO3 231 231 100 28.4 10.0 59
Hardness <200 as CaCO3 233 233 100 31.8 13.5 64.3
Turbidity <5 NTU 940 940 100 0.887 <0.1 8.8
Colour <15 Pt-Co 940 940 100 4.56 <0.1 12
Chlorine <5 mg/L 940 940 100 0.43 <0.01 1.84
Fluoride <1.2 mg/L 234 234 100 0.90 0.79 1.1
THMs <250 µg/L 232 95th percentile = 114 mg/L
Aluminium <0.2 mg/L 234 233 99.6 0.054 0.00900 0.22
Iron <0.3 mg/L 940 940 100 0.073 <0.02 0.50
Manganese <0.1 mg/L 940 940 100 0.013 <0.0005 0.24
Copper <2 mg/L 940 940 100 0.028 <0.001 1.70
Lead <0.01 mg/L 940 940 100 0.0005 <0.0002 0.047
Total coliforms 0 CFU/100mL(a) 940 923 98.2 0(c) 0 36
Faecal coliforms 0 CFU/100mL(b) 940 940 100 0(c) 0 0

Notes: (a) in 95% of samples; (b) in 98% of samples; (c) median value.
Key: CaCO3 = calcium carbonate; CFU = colony-forming unit; mg/L = milligrams per litre; NTU = nephelometric turbidity units; mL = milliliters; Pt-Co = platinum-cobalt units; THMs = trihalo methanes; µg/L=micrograms per litre.
Source: ActewAGL Annual Drinking Water Quality Report 2003–04.

Table 2: Drinking water quality monitoring results, 2004–05
Parameter Target/Units No. of samples No. meeting target % meeting target Mean Min Max
pH 6.5–8.5 942 849 90.1 8.10 7.2 9.3
Alkalinity <200 as CaCO3 237 237 100 35.8 10 63
Hardness <200 as CaCO3 237 237 100 39.6 10.5 68.4
Turbidity <5 NTU 942 940 99.8 0.47 0.1 4.4
Colour <15 Pt-Co 943 943 100 2.38 1.0 14
Chlorine <5 mg/L 944 944 100 0.69 <0.01 3.62
Fluoride <1.2mg/L 236 236 100 0.91 0.07 0.98
THMs <250 µg/L 235 95th percentile = 93.6 mg/L
Aluminium <0.2 mg/L 237 237 100 0.033 0.015 0.19
Iron <0.3 mg/L 942 938 99.6 0.0325 0.02 0.59
Manganese <0.1 mg/L 942 938 99.6 0.0104 0.0012 0.13
Copper <2 mg/L 942 942 100 0.0182 0.002 0.29
Lead <0.01 mg/L 942 940 99.8 0.0004 0.0002 0.026
Total coliforms 0 CFU/100mL(a) 944 942 99.8 0(c) 0 15
Faecal coliforms 0 CFU/100mL(b) 944 944 100 0(c) 0 2

Notes: (a) in 95% of samples; (b) in 98% of samples; (c) median value.
Key: CaCO3 = calcium carbonate; CFU = colony-forming unit; mg/L = milligrams per litre; NTU = nephelometric turbidity units; mL = milliliters; Pt-Co = platinum-cobalt units; THMs = trihalo methanes; µg/L=micrograms per litre.
Source: ActewAGL Annual Drinking Water Quality Report 2004–05.

Table 3: Drinking water quality monitoring results, 2005–06
Parameter Target/Units No. of samples No. meeting target % meeting target Mean Min Max
pH 6.5–8.5 947 869 91.8 8.1 7.2 9.2
Alkalinity <200 as CaCO3 235 235 100 41 4.0 59
Hardness <200 as CaCO3 235 235 100 42 28 70
Turbidity <5 NTU 951 951 100 0.26 <0.1 1.9
Colour <15 Pt-Co 951 951 100 0.92 <1 4.0
Chlorine <5 mg/L 951 951 100 0.63 <0.01 1.66
Fluoride <1.2mg/L 239 239 100 0.84 0.11 1.1
THMs <250 µg/L 234 234 95th percentile = 50 mg/L
Aluminium <0.2 mg/L 235 235 100 0.038 0.015 0.13
Iron <0.3 mg/L 951 951 100 0.013 <0.02 0.17
Manganese <0.1 mg/L 945 945 100 0.006 0.0006 0.10
Copper <2 mg/L 945 945 100 0.012 <0.001 0.17
Lead <0.01 mg/L 945 945 100 0.0002 <0.002 0.0036
Total coliforms 0 CFU/100mL(a) 951 951 100 0(c) 0 0
Faecal coliforms 0 CFU/100mL(b) 951 951 100 0(c) 0 0

Notes: (a) in 95% of samples; (b) in 98% of samples; (c) median value.
Key: CaCO3 = calcium carbonate; CFU = colony-forming unit; mg/L = milligrams per litre; NTU = nephelometric turbidity units; mL = milliliters; Pt-Co = platinum-cobalt units; THMs = trihalo methanes; µg/L=micrograms per litre.
Source: ActewAGL Annual Drinking Water Quality Report 2005–06.

Table 4: Drinking water quality monitoring results, 2006–07
Parameter Target/Units No. of samples No. meeting target % meeting target Mean Min Max
pH 6.5–8.5 959 941 98.1 7.90 6.4 9.3
Alkalinity <200 as CaCO3 240 240 100.0 44 28 76
Hardness <200 as CaCO3 240 240 100.0 47 28 80
Turbidity <5 NTU 959 959 100.0 0.31 <0.1 3.0
Colour <15 Pt-Co 959 959 100.0 1.2 <1 4.0
Chlorine <5 mg/L 959 959 100.0 0.58 <0.01 2.0
Fluoride <1.2mg/L 239 237 99.2 0.79 0.11 1.3
THMs <250 µg/L 243 243 95th percentile = 0.084 mg/L
Aluminium <0.2 mg/L 240 239 99.6 0.040 0.009 0.22
Iron <0.3 mg/L 959 959 100.0 0.0150 <0.02 0.23
Manganese <0.1 mg/L 959 957 99.8 0.010 0.0006 0.27
Copper <2 mg/L 959 959 100.0 0.021 <0.001 1.7
Lead <0.01 mg/L 959 958 99.9 0.0003 <0.0002 0.074
Total coliforms 0 CFU/100mL(a) 959 955 99.6 <1(c) <1 26
Faecal coliforms 0 CFU/100mL(b) 959 959 100.0 <1(c) <1 <1

Notes: (a) in 95% of samples; (b) in 98% of samples; (c) median value.
Key: CaCO3 = calcium carbonate; CFU = colony-forming unit; mg/L = milligrams per litre; NTU = nephelometric turbidity units; mL = milliliters; Pt-Co = platinum-cobalt units; THMs = trihalo methanes; µg/L=micrograms per litre.
Source: ActewAGL Annual Drinking Water Quality Report 2006–07

Data sources and references

Information for this indicator was obtained from ActewAGL's Annual Drinking Quality Reports.

ActewAGL, ActewAGL Drinking Water Quality Report 2003–04

ActewAGL, ActewAGL Drinking Water Quality Report 2004–05

ActewAGL, ActewAGL Drinking Water Quality Report 2005–06

ActewAGL, ActewAGL Drinking Water Quality Report 2006–07

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