3.7
POTABLE USE OF RAINWATER (WATER DISTRIBUTION SYSTEMS)
It is critical that rainwater that will be used for potable use within the public water distribution system
HEALTH AND SANITATION
meets the same criteria as that of other sources of water used in the water distribution system (Table
3.4). Once source water (in this case rainwater) has been shown to be of a potable standard for use
in a public distribution system, there are other inbuilt mechanisms within a distribution system which
<< then
Continued
25 of water that comes out of the tap is not compromised.
ensure from
that page
quality
27
Table 2: Rainwater use in public water distribution systems: suggested
Table 3.4
Rainwater use in Public Water Distribution Systems: Suggested Minimum Water
minimum water quality guidelines for potable and non-potable use
Quality Guidelines for Potable and Non-potable Use (TRHEC, 2006).
USE
Household
RAINWATER QUALITY FOR NON-
POTABLE USE
Organism Concentration
(cfu/ 100 ml)
Total coliforms < 500
Faecal coliforms
< 100
RAINWATER QUALITY FOR POTABLE
USE
Organism
Concentration
(cfu/ 100 ml)
Total coliforms 0
Faecal coliforms 0
Protozoan cysts 0
Viruses 0
Turbidity ( NTU)
< 0.3
One such system is the Blue Drop certification programme which is a nationwide programme
designed with a list of regulatory criteria which when implemented in conjunction with South African
Drinking Water guidelines (DWAF, 1996), ensures that excellent drinking water is produced by a
given water distribution system.
underground. Tanks that are stored underground process and hence it is preferable to have the
lowest turbidity as possible for drinking water,
should be located 15 meters away from
3.8 POST HARVESTING TREATMENT OF RAINWATER
preferably <1 Nephelometric Turbidity Units
animal
breeding grounds and any wastewater
(NTU).
treatment-related
activity.
Constant monitoring of the rainwater harvesting system
will ensure that it performs better thereby
producing rainwater of an acceptable quality consistently. Table 3.5 provides a summary of the
different removal methods that should be used throughout the rainwater harvesting system to ensure
POTABLE
USE OF RAINWATER (WATER
NON-POTABLE
OF RAINWATER
that contaminant USE
concentration
is minimised or prevented
altogether.
DISTRIBUTION SYSTEMS)
(INDOOR)
Table 3.5
Treatment and removal methods of contaminants during rainwater harvesting
Non-potable uses (Van
of rainwater
include
flushing
Giesen and Carpenter, 2009). It is critical that rainwater that will be used for
potable use within the public water distribution
toilets, car washes, and also for laundry
METHOD
LOCATION
RESULT
system meets the same criteria as that of other
purposes.
Guidelines
governing
microbial
SCREENING
Leaf Screens and
Prevents
leaves
from
sources of water
used
in and
the other
water debris
distribution
contamination
in Strainers
non-potable Gutters
water and
are downspouts
not as
entering the tank
system.
Once
source
water
(in
this
case
stringent
as
compared
to
that
of
potable
water.
SETTLING
rainwater) has
been
to matter
be of a potable
However,
total coliform and faecal
Sedimentation
Within coliform
tank
Settles
out shown
particulate
FILTERING
standard for use in a public distribution system,
levels
are still defined for non-potable water in
Roof washer
Before tank
Eliminates suspended material
there are other
inbuilt mechanisms within a
order
to ensure a general microbial
quality of
In-line/multi-cartridge
After pump
Sieves sediment
distribution Removes
system that
then reduces
ensure
that the
the Activated
water. charcoal
Total coliform levels After
in non-potable
sediment filter
chlorine,
odour
quality of water that comes out of the tap is not
water should be <500cfu/100mℓ and faecal
14
compromised.
coliform levels <100cfu/100mℓ (cfu = colony
forming units).
One such system is the Blue Drop
Certification Programme, which is a
POTABLE USE OF RAINWATER
nationwide programme designed with a list of
(HOUSEHOLD LEVEL)
regulatory criteria, which, when implemented
General drinking water guidelines apply
in conjunction with South African Drinking
to the potable use of rainwater as well.
Water Guidelines (DWAF, 1996), ensures that
It is critical that potable water does not
excellent drinking water is produced by a
contain any microbiological contaminants
given water distribution system. PA
after undergoing treatment. There should
be zero amounts of total coliforms, faecal
coliforms, viruses, and protozoan cysts
(Giardia sp. and Cryptosporidium sp.)
found in potable rainwater.
The turbidity of water is an indicator of the
amount of organic and inorganic material,
plankton, clay, and silt in a particular water
sample. A high turbidity level of a particular
water sample is often linked with a greater
chance of microbial contamination. Turbidity
often interferes with the water disinfection The turbidity of water is
an indicator of the amount
of organic and inorganic
material, plankton, clay,
and silt in a particular
water sample.
www.plumbingafrica.co.za March 2018 Volume 24 I Number 1