Greywater reuse systems for regional areas

Different climates and soil types need to be considered when designing greywater reuse systems in regional areas. For example, in northern WA, water use for garden irrigation can be much higher than in the Perth metropolitan area (Water Corporation, 2010), and so the potential benefits from greywater reuse are also greater. Some of the most important factors for consideration are outlined here.

Climate

Many areas of WA experience low and inconsistent rainfall, as well as high levels of evapotranspiration resulting in a higher water demand for plant survival than in Perth. While there is greater potential to make scheme water savings, any greywater reuse system must be designed with particular attention to meeting plant water requirements.

Soil type and permeability assessment

While the Swan Coastal Plain predominantly comprises highly permeable sands, regional areas in the state tend to be much less sandy and contain varying amounts of clay. The percentage of clay is described by the degree of reactivity (swelling/contracting) and also impacts the soil’s permeability. In addition, clay soils are structurally affected by both pH and the amount of salts in any applied water.

The local scheme water supply in some regional areas, particularly where it is sourced from groundwater, can also contain elevated concentrations of dissolved minerals (salts). This is exacerbated in hot and dry climates as salts can build up in the soil over time due to evaporation which requires occasional flushing with fresh water to reduce this effect.

A correct assessment of the soil type and its permeability by a greywater professional in accordance with the relevant Australian Standard (AS/NZS 1547:2012) will ensure that the greywater irrigation area is correctly sized for the available water.

Management

Over the longer term, management is the key to successful greywater reuse in regional areas:

• Use low salt detergents and other household products.

• Regularly apply soil conditioner and mulch to the irrigation area to increase humus content and to improve / maintain soil structure and permeability as well as buffer pH.

• Design the garden and greywater irrigation system to allow for zones of the garden to be rested from greywater application.

• Select salt and alkaline tolerant plant species for landscaping.

• Consider diverting laundry greywater (which is typically the most concentrated) directly to sewer so that only greywater from the shower and bathroom enters the greywater re-use system.

• Consider increased setbacks from the building beyond the recommended 0.5 metre limit for delivery of the greywater via sub-surface/strata irrigation.