Evidence of global warming in response to rising atmospheric carbon dioxide and other greenhouse
gases levels is accumulating [1,2]. Based on atmospheric ocean-coupled global circulation models
(AOGCMs), it has been suggested that a doubling of ambient carbon dioxide (CO2) concentrations
could increase the global mean air temperature by 1.5 °C to 4.5 °C (with high confidence) [2]. Climate
change and global warming will result in increased temperatures, strongly affecting many aspects of
hydrological systems, water resources, coastal zones and oceans [2,3].
Rainwater harvesting (RWH) has been practiced for centuries in many parts of the world. Rainwater
harvesting has been widely accepted around the world as one of the main alternative sources of
water [4–7] and also is considered one of the best practices in combating urban floods. RWH has been
practiced for many years in Sri Lanka. Sri Lanka is a good candidate for practicing RWH due to the
fact that Sri Lanka receives abundant rainfall throughout the year [8]. In the recent past, RWH was
commonly used in the urban context, as well as in rural areas. With the increased trend in urban green
buildings and amendments to recent laws, RWH has become a mandatory requirement of modern
buildings [9]. It is evident that there will be more RWH systems added to the total existing number in
the near future.