Water recycling

The water recycling node serves to implement a representation of catchment-scale wastewater reuse within the modelled project area. The node functions by first activating wastewater recovery at the catchment level, which prompts the model to direct all greywater and blackwater generated by the households situated within the project area to a conceptual storage body. Following this, the parcels contained within the GIS boundary layer used with the node are assigned a number between 0 and 100 – if this number is less than the value set for the water recycling percentage parameter, then the parcel is assumed as eligible for wastewater recycling uptake.

A parcel’s actual utilisation of reclaimed wastewater is dependent on both its eligibility to harness other alternative water sources, and its current uptake of such initiatives. To begin with, rainwater harvesting tanks for non-potable reuse and stormwater harvesting are given precedence, and will always be implemented over water recycling if available to a parcel. In addition, a lot that was assigned an alternative water source in a previous simulation also cannot employ wastewater reuse.

If a parcel has been specified as available to harness reclaimed wastewater and it has not been earmarked for rainwater harvesting or stormwater reuse, it is designated as participating in the water recycling scheme, and its corresponding non-potable and outdoor water demands are aggregated with others at the catchment scale and used as the demand stream for the conceptual storage body.

The storage body operates as a simple bucket or conceptual model, with the daily with the daily greywater/blackwater discharge and aggregated water demands as the inflow and drawdown, respectively. Any surplus in the former is taken as stored volume for that time step, minus the spillage that accounts for the storage body volume (which is set to 20ML for water recycling systems); and the daily demand satisfied by the inflow/stored volume is summed to the annual level – this serves to quantify the amount of water from the water supply network that can be substituted with reclaimed wastewater (owning to the amount of households that participate in the water recycling scheme) on an annual basis.







WR uptake (%)


Percentage of buildings with recycled wastewater


0 - 100