BOM National Performance Report 2020-21:

A wastewater snapshot

Each year the Australian Bureau of Meteorology releases the National Performance Report for urban water utilities, the 2020-21 report is available for public download here: http://www.bom.gov.au/water/npr/

This annual report aims to provide benchmarking of pricing and service quality for urban water utilities. The report is helpful for utilities to monitor annual trends within their own organisations, as well as look at whether their key metrics sit within the typical range in a broader national context. Utilities are grouped within four size categories (small, medium, large, major). This reflects that revenue base and population density can be a factor in both the cost required to provide water and sewer to customers as well as the level of service that is appropriate or sustainable.

Running to 128 pages, this is a comprehensive report that lists metrics across 166 categories from 86 utilities. Dependent on your area of expertise or interest, there is interesting information for everyone.

Figure 1 – Australian utilities that submitted data for the 2020-21 report.

This article summary focuses on some of the key metrics that relate to gravity sewer mains and wastewater expenditure.

Sewer Main Breaks and Chokes

To enable comparative analysis, many of the metrics are reported as ‘per 100km of asset’, this is the case for ‘sewer mains breaks and chokes’.¹ This last year has seen improvements for many locations with 57% of utilities reporting a decrease in breaks and chokes compared to the previous reporting year with Clarence Valley Council, Gippsland Water, and Gladstone Regional Council all seeing reductions of > 75%.

Utilities reporting the lowest instance of breaks and chokes in each utility group size is listed in the table below.

Table 1: Number of sewer mains breaks and chokes per 100 km (Indicator A14)

Utility Group	Utility	Value
Small (10,000 – 20,000 properties)	Water Corporation – Geraldton (WA)	3.4
Medium (20,000 – 50,000 properties)	Tweed Shire Council (NSW)	1
Large (50,000 – 100,000 properties)	Gippsland Water (VIC)	1.5
Major (100,000+ properties)	City of Gold Coast (QLD)	3.8

Major utilities saw the largest improvement for this metric. However, reductions were not the norm for small-sized utilities with the median increasing from 13.7/year to 15.6/year, and the average increasing from 25.3/year to 35.5/year.

Capital Expenditure per Property (Wastewater)

The report notes that the national median per property capital expenditure on wastewater services decreased by 11% from 2019-20 to 2020-21.

Utilities reporting the lowest wastewater expenditure per property in each utility group size is listed in the table below.

Table 2: Capital expenditure per property – wastewater (Indicator F29)

Utility Group	Utility	Value
Small (10,000 – 20,000 properties)	Gympie Regional Council (QLD)	$88.90
Medium (20,000 – 50,000 properties)	Dubbo Regional Council (NSW)	$3.65
Large (50,000 – 100,000 properties)	Power and Water Corporation – Darwin (NT)	$146.72
Major (100,000+ properties)	City West Water Corporation (VIC)	$143.57

Looking more closely at the data split by utility size, the average annual capital expenditure on wastewater is surprisingly similar across all utility sizes; in the region of $275 to $300 per property. The reported figures over the last decade do indicate that small and medium sized utilities may be investing less, on average, on wastewater infrastructure.

While there may be a variety of reasons for this, it will be of some concern if a trend of reduced investment is reflected in a similar reduction in wastewater service level KPIs (including sewer main breaks and chokes).

Figure 2 – Capital Wastewater Expenditure per Property

Despite the significant reported drop in per property wastewater expenditure over the last year (11%); the overall reported capital expenditure on wastewater has remained reasonably stable since 2017 at around $2.7 billion dollars per year – with a drop of 2.9% from 2019-20 to 2020-21 based on reported figures.

Figure 3 – Capital Wastewater Expenditure

Wastewater Operating Cost per Property

The report saw 66 of 86 utilities submit data on operating cost per property to supply wastewater services. The following utilities in each category reported operating their networks at the lowest cost:

Table 3: Wastewater operating cost per property (Indicator F14)

Utility Group	Utility	Value
Small (10,000 – 20,000 properties)	City of Kalgoorlie-Boulder (NT)	$168.96
Medium (20,000 – 50,000 properties)	Rockhampton Regional Council (QLD)	$294.59
Large (50,000 – 100,000 properties)	Toowoomba Regional Council (QLD)	$243.35
Major (100,000+ properties)	South Australian Water Corporation (SA)	$231.92

Residential Wastewater Bill

The cost to provide services is impacted by a wide range of factors, including but not limited to: age of assets, condition of assets, density of population, climate and topography. The table below lists the lowest residential wastewater bill in each category for the 20/21 period.

Table 4: Typical residential wastewater bill (Indicator P14)

Utility Group	Utility	Value
Small (10,000 – 20,000 properties)	Armidale Regional Council (NSW)	$465
Medium (20,000 – 50,000 properties)	Lower Murray Water (VIC)	$491.84
Large (50,000 – 100,000 properties)	North East Region Water Corporation (VIC)	$239.16
Major (100,000+ properties)	City West Water Corporation (VIC)	$347.92

The report indicates 57% of utilities had a reduction in the typical residential wastewater bill with Central Coast Council seeing the largest change (-24%). However nationally, the overall trend was only marginal (<1% decrease).

¹ Wastewater mains breaks and chokes is intended to include:

Gravity sewer mains
Rising (pumped) mains
Low pressure mains
Vacuum system mains

It excludes:

Property connections
Treated effluent mains
Recycled water mains

It can be questioned whether failures on pumped rising mains and chokes within gravity sewer networks should fall under the same metric. While these asset types are intrinsically connected to form the majority of a sewer network, they operate under very different conditions and the mode and cause of failure are often quite distinct.

The information and data for this snapshot is sourced from Part A and Part B of the National performance report 2020–21: urban water utilities. It has been used under the Creative Commons Attribution 3.0 Australian License.

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What are combined sewer overflows?

Image showing heavy rain on a city street

Early underground pipe systems, such as those in the United Kingdom, were built before separation of wastewater and rainwater pipes were common practice. These types of systems are called combined sewer systems.

A combined sewer overflow (CSO) event is the term used to describe when the capacity of the pipe to carry wastewater and rainwater at the same time is too much for the system to deal with, and the system overflows.

The consequence of CSO events can have a very serious impact on the environment and public health. For this reason, most water utilities have a regulator that monitors the performance of the water utilities to ensure pipe networks operate in a safe way. In the United Kingdom, this performance is monitored by the Environment Agency and regulated by OFWAT, who have recently started to undertake further investigations on the release of unpermitted sewage discharges into rivers and watercourses by some UK water companies. In Australia and the USA, the regional Environmental Protection Agency (EPA) organisations regulate and fine water authorities that are not operating in accordance with certain agreed criteria.

What causes a combined sewer overflow?

A combined sewer overflow (CSO) will most likely happen when both the wastewater and surface water experiences high flow at the same time. For example, when there is a lot of rainfall, and a lot of people at home flushing toilets, showering and cooking, placing greater demand on the sewer pipe network.

Picture showing difference in combined sewer overflow over dry and wet weather conditions — *POTW is a publicly owned treatment works
Source: U.S. Environmental Protection Agency, Washington, D.C. “Report to Congress: Impacts and Control of CSOs and SSOs.” Document No. EPA 833-R-04-001

There are lots of factors that can increase the likelihood and occurrence of a Combined Sewer Overflow, such as rainfall, population growth, and pipe condition. With increasing areas of land being paved, an increasingly urban population that each uses ~150L per person per day, and increased intensity of rainfall as the climate changes, the pipe networks built during the 19th century are unable to adapt.

What is the water industry doing about Combined Sewer Overflow?

Most combined sewer systems will be designed to overflow at a specific point in the network that will minimise damage and risk to the public and the environment. Because an overflow would usually occur when there is a high rainfall event, rainwater would dilute the raw sewerage, minimising (but not eliminating) the impact of the overflow. If the system was built without a designed overflow point, then whenever there are high flow events, sewerage may backflow to the nearest exit point, which may be directly into some unfortunate persons’ property.

To tackle this problem, some water utilities have been installing monitoring devices at commonly overflowing points in their pipe network. These devices send a signal to the water companies to let them know if the level of sewage in the pipe/structure is rising more than usual. If the level of sewerage reaches a certain value, an early warning alert is sent to the water company to let them know that an overflow may be imminent so that they can take action if required.

How can spills from combined sewer overflows be prevented?

Adding storage capacity to the network

In addition to some of the initiatives being undertaken by water companies described above, prevention of these types of overflows could also come adding storage capacity to the network. By increasing the capacity of the network to not only convey, but store (for a short period of time), it is possible to reduce the incidence of sewer overflows. This can come in the form of storage/detention tanks for both sewage and surface water.

Increase the treatment capacity of the network

Another option is to increase the treatment capacity of the network so that the sewage can be turned into good quality water faster, leaving more capacity in the network to convey sewage during times of high flow. A key element to the efficacy of treatment in the network to reduce CSO’s is to also make sure the upstream and downstream network from the overflow structure are in optimum condition. If these pipes fail or get blocked, then treatment capacity is greatly reduced.

A great example of increasing the storage and treatment capacity of a combined sewer network to prevent CSOs is the Thames Tideway tunnel. Reconnecting London with the River Thames. This project both increases the storage capacity of the network, and increasing the treatment capacity of the network by routing sewage to an upgraded treatment plant.

Separating the sewer and surface water pipe network

This is an option, though depending on the level of existing infrastructure development not always a practical one. For newer developments, this is a great option to increase the conveyance capacity of a network to a downstream treatment source. A key challenge with separated systems is that regular monitoring of any new building developments is needed to reduce/eliminate illegal surface water connections into the sewer network. These illegal connections are either done mistakenly or deliberately, brought about when a surface water pipe is not available.

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