The components of the TWD can be added to WSUD models as inputs, and along with other data, is used to calculate the amount by which the Total Water Demand (TWD) can be “reduced”. Technically, the TWD is not reduced, only the amount of demand that is supplied by the municipality is reduced, with the remaining portion being supplied through the use of WSUD methods. In essence, it is a reduction on the dependence of municipally supplied water.
METHODS
RAINWATER HARVESTING
WATER EFFICIENT DEVICES
GREYWATER HARVESTING
A third WSUD method that was investigated is the use of water efficient devices (WED) to reduce the indoor TWD. The model was provided by Daniel Coulson. the model calculates the % reduction in water use for each indoor end-use separately, then adds them together to give an average reduction for all indoor end-uses.
The rainwater harvesting (RWH) model calculates the amount of rainwater that can potentially be harvested from the roofs of each property.
The model looks at the cost of implementing the WSUD method and is optimizes the tank size by selecting a size that gives the highest yield of harvested rainwater while keeping the cost per kL below that of municipally supplied water.
This yield can be used to supplement municipally supplied water. The yield is compared with the estimated TWD to determine the % reduction.
Since the Consumption model can calculate the different components of the TWD, it is possible to run the RWH model for different scenarios. 4 different RWH scenarios were chosen, each with a different set of end-uses and/or parameters. Because of issues surrounding the quality of the rainwater harvested, it is not suitable for certain end-uses, unless treated prior to use.
Like the RWH model, the GWH model can also be used to investigate different scenarios. 3 different scenarios were chosen for this model. Again, the quality of the greywater harvested determines which end-uses are suitable.
The greywater harvesting (GWH) model uses the same methods as the rainwater harvesting model. However, instead of considering rainwater runoff as the source, greywater (which is produced by certain indoor end-uses such as baths and showers) is used.
The amount of greywater produced is determined using the TWD model, taking the indoor demand and removing the toilet component, which is considered as blackwater and is not suitable for re-use.
The WED model has 2 different scenarios, which look at the efficiency the devices that is is installed.
WSUD
Water Sensitive Urban Design
