Stormwater Harvesting

Stormwater harvesting is the use of rainfall runoff from developed catchments for water supply. It typically involves the diversion of stormwater from a drainage system to a storage and treatment facility where it is enhanced through a multi-stage treatment process for use in high water using applications such as cooling towers or sports field irrigation.

Stormwater is a poorer quality water source compared to roofwater and environmental approval may be required to divert stormwater. A stormwater harvesting system can deliver significantly greater water savings than a roofwater harvesting system as runoff is diverted from both roof and non-roof catchment areas.

A sites topography and drainage network dictate how stormwater can be diverted into a harvesting system and the diversion system can be a significant cost component. Storage is also a major cost component and optimising capacity is a focus of design.

The stormwater treatment process varies depending on raw water quality and end use requirements, however it typically involves media filtration and disinfection. A centralised control system with a network of wireless sensors allows harvesting systems to be fully automated with quick detection of performance issues and easy tracking of water savings.

Key engineering considerations for stormwater harvesting systems are summarised further below and in the attached brochure.

Stormwater needs to be diverted away from the catchment drainage system and into storage. The system used to divert the stormwater depends on the diversion point but typically consists of a diversion weir, pumping station and a pipeline to a storage facility.

Key considerations:

Diversion point and catchment area

Diversion capacity

System needed to divert stormwater without increasing flooding risks

Storage is required to hold captured stormwater until it is needed for use. Tanks are the most common form of storage however open surface structures such as small dams are also used.

The treatment process varies depending on the raw water quality and the end use, however it typically involves media filtration to reduce cloudiness and UV or chlorination disinfection.

Key considerations:

Need for raw and treated water storage

Storage and treatment facility location and capacity

Pre-screening mechanism and aperture

Level of filtration, disinfection and chemical adjustment needed to meet end use requirements
Supplying stored water to the application point requires delivery pumps and a dedicated non-potable water delivery line. A back-up potable water supply is commonly incorporated into the distribution system to ensure water is always available.

Key considerations:

Delivery pump type and activation mechanism

Need for and location of potable back-up

The level of control required for a stormwater supply system varies depending on the end uses being serviced and the complexity of the system. A typical stormwater harvesting system uses a master programmable logic controller (PLC) interfaced with sub PLCs that control individual system components. The master PLC supervisors all system components and decides when water can be moved between different parts of the system.

Control capability and required level of system automation

Alarm management requirements

Type and number of sensors and control hardware