The sustainability app models water demands using a bottom-up approach – water demand is broken up into end-uses, each of which are estimated using an intensity.
Hourly profiles of water demand distribute daily values to hourly values.
Water supply is resolved through an hourly model that balances inflows, outflows, storage and spills of different water grades.
Water grades
Water grade is modelled as a hierarchy. Each end-use has a minimum grade it can be serviced by, but can accept all grades of water above its minimum grade.
Potable: Suitable for drinking purposes such as fixtures, baths and showers. Also suitable for appliances, toilet flushing and irrigation.
Non-potable: Suitable for non-drinking purposes such as clothes washing, toilet flushing and also irrigation.
Irrigation grade: Suitable only for irrigation.
Demand
Demand is estimated for each end-use using an intensity based approach. Intensities are hard coded and may vary for different usage items, different locations and different item settings. Intensities quantify water demand as a volume per resident for most residential end-uses or per square metre for non-residential and irrigation end-uses.
Residential
Residential usage items include detached and terrace houses as well as low-, mid- and high-rise apartments. Demand is based on the estimated number of residents, as well as water efficiency ratings.
End-uses include:
Taps (kitchen, laundry and other)
Showers and baths
Toilet flushing
Clothes washing
Dish washing
Leaks
Pools
Car washing (houses only)
Non-residential
Demand is based on the type of non-residential item (e.g. commercial, retail, shopping centre, school etc.), a single efficiency setting and floor area. End uses include fixtures and appliances.
Irrigated spaces
Includes public spaces like parks and plazas as well as private spaces like detached and terrace house gardens and apartment common area gardens.
Demand is based on the level of irrigation required to maintain the specific space type. Non-residential irrigation rates use Sydney Water guidelines (extrapolated for climate zones outside of Sydney using pan-evaporation). Residential irrigation rates are based on average household external water use.
Annual values are distributed to daily values using a model that relies on typical weather data for the location (pan evaporation, dry-bulb temperature and rainfall), and to hourly values using profiles that differ based on whether or not the rainfall for the day is zero.
Supply and storage
Different supply systems provide water at different grades.
Mains water supply provides potable grade water. There is no limit to how much can be supplied.
Rain water systems provide either potable or non-potable grade water (depending on the “Output grade” selection) and can only supply as much as they have stored in their tanks.
Recycled water systems provide either potable or non-potable grade water (depending on the “Output grade” selection) and can only supply as much as they have stored in their holding tanks. There is a certain level of treatment loss given by the “Loss factor proportion” setting.
Supply of water of different grades is modelled hourly by balancing:
Inflows: water entering the system from rainfall or sewage collection and treatment
Outflows: the demand placed on the system for each grade
Storage: the capacity and level of holding tanks, and
Spills: when inflows exceed outflows and storage is at capacity.
Demands for grades are first met by their minimum grade, then if insufficient, by a grade higher, until all demand is met. It is assumed that all demand can be met by mains water if required meaning there is no possibility of unmet demand.
Rain water inflows
The quantity of rain water in millimetres is modelled using typical weather data for the location and time of year.
The volume harvested from rainwater is given by the number of millimetres of rain experienced multiplied by the area of the collection area (generally a building’s roof) that is connected to the rainwater tank system. Tank volume is measured on a daily basis taking into account the previous day's volume, daily inflow and daily demands.
Recycled water inflows
Recycled water is fed by the sewage outflows of the connected spaces. This amount is reduced by an assumed level of treatment loss (which counts as a spill).
Sewage volumes are estimated for each end-use by factoring in a retention rate for the given end-use. Most retention rates are 100% except for irrigation, pools and leaks which are 0%.
Mains water inflows
All demand that is unmet by onsite recycled or rain water systems is met by potable mains water.
Hot water and energy
Some end-uses have a hot water demand. The water grade required for hot water is potable water, and depending on the configuration of the end-use an energy demand (as either electricity or gas) is estimated. For example, showers connected to a gas instant hot water system have a demand for (potable grade) water and natural gas.