Most roofs are suitable however there are a number of contamination issues that need to be considered including waste from human access, atmospheric pollution, chemical contamination from roofing materials and biological contamination due to birds or devices such as cooling towers.

1. Storage Tanks
Storage tanks are often a significant cost component of roofwater harvesting systems and selecting an
appropriate capacity is a focus of design. Roofwater storage tanks are typically above ground steel,
polyethylene or fibreglass tanks. Below ground precast concrete or fibre-reinforced plastic (FRP) tanks
are also used where above ground tanks are not suitable.
STORAGE AND TREATMENT
Storage is needed to balance irregular rainfall with typically
regular demand for water. Roofwater is screened before
entering storage tanks and depending on the application, it
is also typically passed through a filtration and disinfection
system before use.
Suitable Roofs
Most roofs are suitable however there are a number of contamination issues that need to be
considered including waste from human access, atmospheric pollution, chemical contamination
from roofing materials and biological contamination due to birds or devices such as cooling towers.
Diverting Roofwater
Bends are typically inserted in to downpipes to divert roofwater. The diversion point can be at high or
low level, depending on the location of downpipes and storage tanks and if diversion pipes can be
supported to a building wall.
ROOFWATER HARVESTING
Roofwater harvesting is the use of rainfall
runoff from roofs for water supply. It typically
involves the diversion of roof downpipes in to
above ground storage tanks where the roof-
water is filtered and disinfected for use
in non-potable applications such as toilet
flushing and landscape irrigation.
DIVERSION
Roofwater firstly needs to be diverted in to the harvesting system.
This requires access to suitable roofs and the ability to divert
roof downpipes in to storage.
Alternative
Water Solutions

2. Pre-Screening and First Flush
Roofwater is screened prior to entering the harvesting system to remove debris such as leaves. Gutter
mesh, rain heads and storage tank inlet screens are common. First flush devices are also used to trap
built-up roof silt and leaves from the initial rainfall runoff.
Treatment
A typical treatment process involves micro strainer filtration and UV disinfection. Particular end uses
such as cooling towers may require further chemical treatment. Larger storage tanks may also require
a constant circulation system to prevent the build-up of poorer quality water low in oxygen.
DISTRIBUTION
Getting 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 delivery
line to ensure water is always available.
Delivery Pumps
Pressure pumps that activate each time an outlet is opened in the distribution system are the most
common delivery pump. An alternative is a pressure vessel pump that pressurises a spherical vessel
rather than directly pressurising the distribution system. This system results in fewer pump starts
however also delivers fluctuating pressures.
Potable Back-Up
Most roofwater harvesting systems have a back-up mains water supply that either tops-up the
storage tanks or feeds directly in to the distribution system.
MONITORING AND CONTROL
The level of control required for an alternative water
supply system varies depending on the end uses being
serviced. Most systems are controlled by a small
programmable logic controller (PLC) using a network of
sensors.
Storage
Levels
Distribution
Pressures
Delivery
Pump
PLC
PLCs
A PLC is a small computer used to automate system processes that typically sits in a cabinet with the
treatment and delivery plant. PLCs also store data such as pump run times and flow meter readings
which can be useful in making maintenance decisions and tracking water savings.
Sensors
Pressure sensors are used to activate the delivery pumps when a drop in pressure is detected in the
distribution network. Ultrasonic level sensors or float switches are also used to monitor storage levels
in storage tanks and activate the back-up mains water supply.
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