Newsletter and Technical Publications
Rainwater Harvesting And Utilisation
An Environmentally Sound Approach for Sustainable
Urban Water Management: An Introductory Guide for Decision-Makers
Must be Considered From Quality and Health Aspects in Utilising Rainwater?
In the past, it was believed that rainwater was pure and could be consumed
without pre-treatment. While this may be true in some areas that are relatively
unpolluted, rainwater collected in many locations contains impurities. Particularly
during the last three decades, acid rain has affected the quality
of the collected water, to the point where it now usually requires treatment.
Rainwater quality varies for a number of reasons. While there are widely accepted
standards for drinking water, the development of approved standards for water
when it is used for non-potable applications would facilitate the use of rainwater
In terms of physical-chemical parameters, collected roof water, rainwater and
urban storm water tend to exhibit quality levels that are generally comparable
to the World Health Organisation (WHO) guideline values for drinking water.
However, low pH rainwater can occur as a result of sulphur dioxide, nitrous
oxide and other industrial emissions, hence air quality standards must be reviewed
and enforced. In addition, high lead values can sometimes be attributed to the
composition of certain roofing materials thus it is recommended that
for roof water collection systems, the type of roofing material should be carefully
A number of collected rainwater samples have exceeded the WHO values in terms
of total coliform and faecal coliform. The ratios of faecal coliform to faecal
streptococci from these samples indicated that the source of pollution was the
droppings of birds, rodents, etc.
Currently, water quality control in roof water collection systems is limited
to diverting first flushes and occasional cleaning of cisterns. Boiling, despite
its limitations, is the easiest and surest way to achieve disinfection, although
there is often a reluctance to accept this practice as taste is affected. Chlorine
in the form of household bleach can be used for disinfection, however the cost
of UV disinfection systems are usually prohibitive. One promising area of research
is the use of photo-oxidation based on available sunlight to remove both the
coliforms and streptococci.