Page 56 - Green Builder Sept-Oct 2019 Issue

two facilities respectively, the “slight water savings” at
Ikar were found to be unprofitable.
It is accepted that volumes of precipitation, the
demand for non-potable water, roof surfaces and tank
capacity all affect the efficiency of RWH systems. But
this study showed that there are a huge number of
financial parameters that may potentially influence
the efficiency of any RWH system.
Quite clearly, the financial viability of the two
rainwater harvesting systems studied was impacted by
their efficiency. For instance, during the wettest year
(2010) when rainfall was higher, tests for tank capacity
showed that 29 percent (at Nemcova) and 40 percent
(at Ikar) more rainwater was taken. Even though the
percentage of rainwater discharged into the sewer
systems during the same year was very similar (85
percent at Nemcova and 87 percent at Ikar), water
savings were 36 percent and 23 percent, respectively.
In 2003, the driest year, the savings at Nemcova were
25 percent, which was even more than Ikar’s savings
in the wet year!
One factor the researchers highlighted was that
while water-flushing demands were exactly the
same, the water surface area from which the water
was collected at Ikar was significantly lower than
Nemcova. The slightly bigger tank size at Nemcova
was found to be an advantage.
Other factors that impacted on the two rainwater
management systems included operating costs. Also,
capital expenditure at Ikar was unacceptably high.
The total period of analysis was 30 years, but the
researchers agreed that a longer functioning period of
CREDIT: EDSEL LITTLE/FLICKR 50 years for an RWH system, as suggested by previous
research, would lead to a more favorable investment.
Generally, plastics used to manufacture tanks suitable

years, so that wasn’t an issue.
Taking up a collection. A rainwater collection system doesn’t have to be high tech—it can be as for RWH systems have a minimum life span of 50
simple as a barrel set up to capture downpours. Ultimately, Stec and Zelenáková concluded that
rainwater harvesting has many benefits for the
Precipitation from 2003 to 2012 was analyzed and found to be similar sustainable development of cities and the environment. Furthermore,
in both places. they can also be financially viable. But because of the influence of
Two financial ratios were used to determine profitability: financial parameters on financial efficiency, it is vital to undertake
■ Net present value (NPV) that shows projected earnings vs full economic and technical analysis to ascertain whether the system
■
anticipated costs and cash flows and ultimately determines future will be profitable or not.
profit. Of course, design engineers realize how important it is to
■ Discounted payback period (DPP) that indicates how long it will determine volumes of water that can potentially be harvested. As
■
take to break even. the Stec/Zelenáková study shows, this can vary tremendously year-
Strangely, while there was so much in common at the two on-year. It’s also recognized that because objectives relating to the
dormitories, implementation of the two systems yielded very primary purposes of RWH systems can conflict (for instance wishing
different results. The Polish RWH system was found to be completely to maximize water saving as well as empty tank volumes for control
unprofitable, with a DPP period that exceeded 30 years. The Slovakian of runoff), systems do require customization to maximize ROI. GB
RWH system, on the other hand, produced favorable NPV and DPP
results. Michael Tobias is the founder and principal of New York Engineers,
Although the researchers concluded that it was possible to save an Inc 5000 Fastest Growing Company in America, with offices in New
around 18 percent and 29 percent water over a 10-year period for the York and Chicago.

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