Rainwater Harvesting Emerges as Global Necessity

(MENAFN) As drought conditions intensify and pressure on global water supplies reaches critical levels, rainwater harvesting systems — designed to collect and store rooftop runoff — are rapidly gaining recognition as a sustainable strategy to curb water consumption and deliver meaningful savings for households and societies alike.

Guclu Insel, a professor at Istanbul Technical University (ITU), told media that such measures have crossed the threshold from optional alternative to outright necessity, driven largely by the erratic precipitation patterns now associated with climate change.

Insel described rainwater as a valuable natural resource that, while relatively pure when it first forms in the atmosphere, risks contamination from air pollution and dust before it ever reaches the ground. "It must be utilized with appropriate filtration and pre-treatment systems," he said.

He underscored the urgency of building adequate storage infrastructure capable of capturing rainfall the moment it occurs, warning that insufficient capacity leads directly to preventable water loss. While tempering expectations about the technology's limits, he was clear about its strategic value. "Rainwater harvesting alone does not solve the entire water problem, but it is a complementary and strategic tool for sustainable water management," he added.

Eyup Arslan, general manager of Hydrain — a rainwater harvesting and water management engineering company — described such systems as a dual-purpose solution built to cushion the blow of both drought and flooding while curbing uncontrolled surface runoff. He noted that while Germany, Australia, and other European nations have long integrated these systems into standard practice, they remain a relatively recent development in Türkiye.

Arslan walked through the mechanics: "Rainwater from the roof is largely cleared of mud and coarse pollutants via filters placed in downpipes and taken into storage tanks. Contaminated water is separated and discharged into the sewage system."

The numbers make a compelling case for widespread adoption. Toilet flushing alone accounts for 35% of household water use, Arslan noted. "A family of three consumes an average of 600 liters of water daily. About 200 liters of this is used in toilet cisterns, which can be met with rainwater. Filling cisterns with rainwater can reduce total water consumption by 30 to 35%. It can also be easily used for park and garden irrigation, building cleaning, and car washing," he said.

The agricultural case is equally strong. Because harvested rainwater contains no salt or chlorine and is naturally rich in nitrogen and nitrate, it is particularly well-suited for crop irrigation. Arslan explained that storage systems are typically positioned in dry creek beds or other strategic locations to capture heavy rainfall for use during dry seasons, often operating entirely without pumps.

On a larger scale, underground storage units can hold between 100 and 50,000 cubic meters of water, with flood-prevention infiltration tanks reaching capacities as high as 500,000 cubic meters. Arslan said these concrete-free, green-technology systems cut mains water consumption by around 30% — with that figure climbing significantly in larger residential complexes. "Savings can reach 40% when used for gardens and common areas, and up to 50% when toilet cisterns, washing machines, and dishwashers are included," he said.

Zooming out to Istanbul specifically, Arslan estimated that the city's 1 million buildings could collectively harvest 100 million cubic meters of rainwater each year — five times the storage capacity of Alibeykoy Dam. Capturing water at the source, he argued, simultaneously addresses conservation and flood prevention.

Yet financing remains a significant barrier. Incentive structures currently operate mainly through organized industrial zones and municipalities, leaving individual homeowners largely dependent on green certification or eco-friendly housing loans from banks. Arslan called for a meaningful expansion of support mechanisms to ensure private residences are not left out of the equation.

He closed with a stark warning against complacency, cautioning that Istanbul risks squandering approximately 100 million cubic meters of water annually without decisive action — and arguing that the systems effectively fund themselves through flood damage reduction. "It's not only water saving but also a disaster prevention solution; it has the potential to reduce the impact of floods by up to 75%. We need to collect water where it falls, not where it overflows," he said.

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