The incredible challenge of water-positive development in rural Australia

Castlemaine in regional Victoria currently has the first two registered Living Building Challenge multi-residential building projects in the world – the Paddock and Bull Street.

• See Hunters and Collectors find Living Building niche in Castlemaine and Castlemaine grows its eco hotspot reputation with second Living Building Challenge project

Both are tracking well and will be under construction this year. Many of the Living Building Challenge petals have been designed in without too much trouble. This is because the fundamental starting point for the architects was to create projects that are of benefit to Castlemaine and its ecosystems.

Yet one petal, the water petal, has been an incredible challenge. The water petal states:

Project water use and release must work in harmony with the natural water flows of the site and its surroundings.

One hundred per cent of the project’s water needs must be supplied by captured precipitation or other natural closed loop water systems, and/or by recycling used project water, and must be purified as needed without the use of chemicals.

All stormwater and water discharge, including grey and black water, must be treated onsite and managed either through reuse, a closed loop system, or infiltration. Excess stormwater can be released onto adjacent sites under certain conditions. (LBC 3.1)

The challenge of reaching this “water positive status” is further increased when it is also the aim to increase density, use energy effectively and sparingly, use no chemicals and be affordable.

This article focuses on the Paddock project and shares how it could work so that other developments in rural Australia can implement similar strategies.

The Paddock is a 27-lot environmentally aware housing development planned to be built in three stages on a 1.4-hectare site at Reckleben Street, Castlemaine. The fully developed site will comprise up to 27 8.5-star energy-efficient homes and a community centre. The homes are planned around a central dam, wetland and productive garden space, with gardens comprising more than 60 per cent of the total site area. These include vegetable plots, native gardens and orchards.

The Paddock is aiming to meet the LBC water positive imperative, but the local conditions makes it difficult as it rains heavily for short periods of time and most of the time it is dry with some years only getting 430mm of rain.

Normally a town would not have evolved in a place with such low rainfall but Castlemaine began because of gold, and this wonderful, vibrant place that has emerged now needs to face its water restricted legacy if it wants to thrive into the future.

For the Paddock two consultants have worked with the project to test how to meet these challenges. Detailed design and implementation of the final option was done by Geoff Clarke of Vivid Civil Engineering, while Robyn Overall at CJ Arms looked at using natural processes to achieve the water petal.

To achieve the water petal three designs were developed for the site.

The first design proposed was a mechanical system that was found to be too expensive, required ongoing maintenance and a lot of energy. As such this was rejected by Coliban and the project team, shifting the project to the second option, which was capturing rain and stormwater and use of grey water on the gardens.

Currently, for this project, both connection to sewer and mains water needs to occur to meet regulations. Therefore the second design ensures that the connection to sewer is through a single point, giving the potential for a treatment system in the future. This second design, however, will not meet the LBC water petal.

Therefore a third scheme was developed by CJ Arms – a grey and blackwater system that can be delivered at a much lower cost than the mechanical system, with little energy use and the ability to meet the water petal.

The design is outlined below:

1. Supply potable water with harvested roof water (1423 square metres). This strategy is adequate to meet demand in above average rainfall years, and could be supplemented with mains water during very dry years. Alternatively, roof catchments could be increased by providing covered carports to residents and collecting rainfall runoff from the additional roof catchment. About 2260 sq m of total roof area is required to meet all potable demand with roof water in below average rainfall years.
2. Wastewater (combined greywater and blackwater streams) is captured and treated through an onsite passive vegetated (reedcell) treatment system. Disinfection provided by a tertiary treatment stage with treated water available for non-potable reuse.

The reedcell system is a passive wastewater treatment system designed for Australian conditions. The reedcells are living planted systems that can be integrated into the surrounding landscape and fit well with the development’s design and its surrounding environment.

An appropriate reedcell system for the Paddocks would require 250 sq m of treatment area and would manage all wastewater (combined blackwater and greywater). Reedcells are biological systems and provide secondary treated water and some nutrient removal, in particular carbon and nitrogen.

Tertiary treatment is required to produce treated water suitable for reuse, and would include:

• Carbon filtration (biologically activated carbon filter or BAC) for removal of dissolved aromatics, removal of colour, and improved UV transmissivity
• Microfiltration for removal of microbiological contamination
• Ultraviolet (UV) disinfection for second barrier removal of microbes

The reedcell system offers advantages of:

• Cost: Compared with a conventional system (say a membrane bioreactor (MBR) or moving bed bioreactor unit (MBBR)) the capital cost for a reedcell system is significantly lower, and operational costs are also lower. This means that the combined reedcell/tertiary treatment system produces water at a cost per kL of water much lower than that produced by the comparable conventional treatment system.
• Low energy: Estimated energy consumption by the proposed passive wastewater treatment system is less than 1kWh per kL of water produced
• Reduced carbon emissions: Up to 80 per cent less carbon emissions, primarily due to the reduced need for mechanical aeration of the water during treatment.
• Zero chemical use: Membrane-based mechanical treatment units required chemical scouring of membranes during routine maintenance, which is not required by reedcells.

3. This treated water would then be used to supply household non-potable demand (toilets and laundries) with recycled wastewater.
4. With the excess treated wastewater disposed of via irrigation at a low rate onsite (500 sq m) and used as a backup irrigation supply to supplement retained stormwater. At the Paddock this area is made up of the orchard and the edge ornamental plantings.

Using option 3 will mean that we can achieve the intention of the LBC water petal with no water going to sewer and no water coming from mains, but we will still need to be connected to both to meet planning and regulatory requirements.

It is important for all projects to continue to strive to meet the LBC challenge and advocate to authorities to revisit how water systems are designed into our developments.

The Paddock is the exception, not the rule, and other developments risk leaving a negative legacy for future generations.

Dominique Hes is director of Thrive Research Hub at the University of Melbourne. Robyn Overall is water sustainability specialist at CJ Arms and Associates.