Central systems

Fire sprinklers

Fire sprinkler test water is water used to periodically test a building's automatic fire sprinkler system. Instead of pumping the water used to periodically test a building's fire sprinkler system into the sewerage system, a closed system is a system where this water can be stored in a storage tank (or similar) to reuse in the next periodic fire sprinkler test.

If the water is partially or completely diverted to a tank for purposes other than fire sprinkler tests (such as garden watering), the system cannot be considered as a closed system.

Image of fire sprinklerFire spinkler. Source: Department of Planning & Environment 

Central water tanks

A central water tank is used in a multi unit development to supply water to common area uses (such as landscaping, car washing bays or cooling towers) or to more than one dwelling, for private garden watering, toilet flushing or laundry. A central tank can collect rainwater and/or stormwater.

A central water tank may collect water from:

  • the roof– of any number of unit blocks or dwellings in the development;
  • impervious areas– surfaces that do not allow natural infiltration of rainfall to the underlying soil and include concrete, gravel and timber surfaces.;
  • garden/lawn areas; and
  • planter boxes.

BASIX assesses central water tanks based on:

  • the area of water collection;
  • the tank size– the volume in litres; and
  • whether the overflow is diverted to another tank;
  • the uses to which the water is allocated.

Water from central water tanks may be allocated to:

  • the area of common landscape served– in square metres;
  • the number of car washing bays; and
  • central cooling systems with cooling towers;
  • private uses for individual dwellings within the development.

There are additional limits to alternative water use from central rainwater tanks, for example it cannot be used for topping up swimming pools or spas. As with individual tanks, untreated water from central stormwater tanks can only be used for sub-surface garden irrigation.

Where a central stormwater/rainwater tank is being designed to service not only the residential development subject to the current development application, but future residential development; or where the central stormwater/rainwater tank is being designed to service both residential and commercial/retail development, the details of the central system must be entered as an "alternative water supply". A hydraulic engineer will need to determine the amount of stormwater and/or rainwater available to the residential component of the current development application (in litres/day).

Central on-site recycled water

An on-site recycled water system is a system that allows for the reuse of greywater or all wastewater (greywater and blackwater) from a site; this includes sewer mining. This alternative water option is only available for multi-unit developments within the BASIX tool.

BASIX assesses central on-site recycled water based on:

  • Supply volume of the central recycled water system
  • Uses of the recycled water, which need to be nominated separately under central systems and as well as under the individual dwellings, if applicable
  • Areas of common landscape supplied by the central on-site recycled water system

Note: On-site recycled water systems require approval from the appropriate consent authorities.

Depending on the level of treatment, recycled water can be used for garden irrigation and some internal uses. The treatment of wastewater must meet relevant treatment standards. All forms of greywater/wastewater are capable of transmitting disease.

The potential uses of the recycled water produced by the central on-site recycling system is determined by the type of wastewater being collected and by the treatment system being operated. Recycled water should not be used for filling swimming pools and spas or for watering edible plants.

On-site recycled water systems should not be used for garden irrigation in areas identified as having major limitations to on-site disposal. Such areas include locations with shallow water tables, highly porous soils (such as sand beds) or with visible signs of surface dampness (such as seeps, soaks or springs).

Some other limitations that must be assessed before adopting greywater/wastewater reuse include soil characteristics, salinity and contaminant loads of wastewater, and the appropriate scheduling of application.

It is necessary to maintain sewer connections to provide an alternative disposal option in the case of on site system failure.

Further information and guidelines on wastewater reuse systems is available from the NSW Department of Health.

Central cooling system

A central cooling system provides cooling for air-conditioning systems in common areas and/or a number of dwellings. A cooling tower is a device for lowering the temperature of water by evaporative cooling in which atmospheric air is in contact with falling water, thereby exchanging heat. Cooling towers consume water through evaporation, bleed, drift, splash and overflow.

There are a number of technical and design strategies that will reduce potable water consumption in cooling towers.

BASIX recognises the following measures:

  • Private water metering
  • Conductivity controllers
  • Using alternative water sources for make-up water

Private water metering

By installing a water meter on the make up line and connecting this meter to a building management system, water loss in your cooling tower or evaporative cooling system using can be monitored and abnormalities in water consumption can easily be detected, minimising water loss through bleed, drift, splash and overflow.

Conductivity controller

A conductivity controller is used to manage the concentration of dissolved solids through the automatic control of water bleed to ensure minimum water loss and maximum water efficiency in a cooling tower or evaporative cooling system.

Make-up water

The make-up water may be supplied from alternative water sources such as rainwater, stormwater and suitably treated recycled water. Recycled water use in NSW is regulated by the NSW Department of Environment and Conservation and by NSW Health. You will need to obtain permission from NSW Health prior to use in cooling towers. The suitability of recycled water as condenser water make up will be dependant upon the recycled water quality.

More information on the water consumption of cooling towers is available in the Sydney Water publication "Water conservation: Best practice guidelines for cooling towers in commercial buildings".


Common landscape area served

As the central water tanks or recycled water system may not be able to provide alternative water to all common landscape areas you will need to tell BASIX the area of common landscape that will be serviced by each central system.

Diagram indicating how to describe the common landscape area serviced by each central water tankDiagram indicating how to describe the common landscape area serviced by each central water tank