HEALTH AND SANITATION
31
Figure 1: Rainwater
can easily be
contaminated through
various sources such
as biological and
chemical matter.
ENVIRONMENTAL CONDITIONS
Environmental conditions are largely out of the
hands of the designer and/or user of rainwater
harvesting systems. Environmental sources of
contamination include anthropogenic sources
of air pollution like industry and major roadways
(Figure 1). Natural sources of contamination
include nearby trees and plants, which deposit
leaves, pollen, etc., and animals (birds, squirrels),
which deposit waste, etc., on the catchment
surface (Figure 1).
(a) Air quality
Rainwater is considered to be contaminant free,
except for pollutants that may be picked up by
rain from the atmosphere. Industrial emissions
and scavenging of airborne microorganisms or
bioaerosols by cloud or rain droplets affect the
quality of harvested rainwater. Air quality can
also be affected by organic pollutants derived
from fuel leakage of vehicles, petrochemical and
plastic-chemical industries, which may in turn
contaminate the harvested rainwater.
(b) Seasonal changes
During dry periods, dust, faecal deposits,
rodents, and birds are the major sources of
heavy pollution. After long dry periods caused
by less rainfall, the quality of harvested
rainwater may be of serious health risks due to
accumulation of these pollutants, especially if
the water is harvested from rooftops. Microbial
contaminants such as E. coli, faecal coliforms,
Salmonella spp. and Giardia lamblia may be
www.plumbingafrica.co.za
detected during this time of harvesting. High
concentrations of microorganisms may be
observed during summer as compared to
colder months.
LOCATION OF THE RAINWATER
HARVESTING SYSTEM
Location of the rainwater harvesting system is
an important aspect to consider when assessing
the level of contamination in harvested rainwater.
In urban areas, rainwater might be already
contaminated before it reaches the catchment
area. This is regarded as the first stage of
contamination, which occurs when rainfall
washes out and scavenges aerosols, gases, and
thin volatile particles from the urban atmosphere.
High levels of heavy metals have been isolated
in harvested rainwater from urban areas as
compared to rural areas. Also, some locations
may receive acid rains as compared to others.
RAINWATER OVERFLOWS
Contaminants can also be introduced into the
rainwater storage tank through the overflow-
handling method used by the rainwater
harvesting system. If overflows are directed to a
municipal storm sewer or an on-site soakaway
pit, there is the potential during intense rainfall
events for these systems to backflow into the
tank, contaminating it with poor quality water.
These overflow-handling systems must be
designed properly and preventative measures
put in place, to minimise the possibility of
storage tank contamination. PA
June 2018 Volume 24 I Number 4