While Israel’s authorities allow almost no decentralized water systems, experts
stressed that there would be a place for such structures – particularly
greywater recycling mechanisms – in the country’s future, at a conference in the
Negev last week.
The third Sde Boker Conference on Advanced Water
Management Technologies was held at Ben-Gurion University Sde Boker
Other highly developed countries, such as the United States,
Australia and Germany, allow at least to some extent the reuse of household
greywater, but the Health Ministry still takes issue with such practices due to
fears of health risk, according to Prof.
Amit Gross, of the Environmental
Hydrology and Microbiology Department at BGU’s Zuckerberg Institute for Water
While Israel reuses a higher proportion of treated wastewater
than any country by far – more than 80 percent – and its desalinated water
industry also thrives, all of these mechanisms are performed in a centralized,
large-scale form. Decentralized greywater reuse, on the other hand, would mean
individual homes reusing sink and shower basin water to flush their toilets and
water their gardens, experts explained.
“In Israel we neglect almost
completely the discipline of decentralized water treatment,” Gross
To put it simply, blackwater is defined as feces with flushing
water and urine, yellowwater is urine with or without flushing water, brownwater
is feces with flushing water without urine, and greywater is other domestic
sewage – such as used shower or sink water, Prof. Jörg Londong of the
Bauhaus-Universität Weimar said.
Londong spoke of projects in Germany and
Switzerland where waste products are being separated into streams right from the
home – deriving nutrients such as nitrogen, phosphorus and potassium from urine,
organic content for biogas and fertilizer from feces, and reusable water from
greywater. The ideal situation, he said, would be “using everything, not just
water but the nutrients.”
About 70% of urban water demand in developed
countries is for domestic consumption, and of that 70%, about 60% to 70% becomes
greywater, said Prof. Eran Fridler, of the Environmental, Water and Agricultural
Engineering Department at the Technion-Israel Institute of Technology.
that greywater, about two-thirds is deemed light greywater – bath, shower and
wash-basin water – and about one-third is dark greywater – water from the
kitchen sink, the dishwasher and the washing machine, Fridler
By using greywater to flush toilets, countries can reduce the
demand for potable water by 30%, and by using it to both flush toilets and water
gardens, countries can reduce the demand by 40%, Fridler said.
planning our systems we have to think about how to save and use more efficiently
our water,” said Eli Cohen, CEO and an engineer at the Tzipori-based Ayala Water
and Ecology, which develops natural biological systems for wastewater
While a centralized approach might be easier to control, it
requires more infrastructure, longer-range transport, more piping, pumping,
maintenance, water loss, energy and contamination, Cohen explained.
Decentralized approaches lack those disadvantages but still are often seen as a
nuisance to the surrounding community and also require complex technological
skill to install, he said.
“It’s starting to get its place in the world,
but it’s too slow,” he said.
Gross and a team have been experimenting
with greywater flow for three years, using installed constructed wetlands for
further purification to irrigate landscapes and gardens. While there have been
failures – only 45% of the systems experienced no failure during the entire
period – fecal coliform levels met stringent Israeli standards, and soil treated
with the greywater was similar in quality to soil treated with freshwater, he
Gross stressed his hope that Israeli authorities would warm up to
the idea of using decentralized greywater systems.
“One major issue is
that there is a lack of long-term quantitative information, and if we introduce
that I think we can convince the authorities that it is possible,” he
On a national scale, using greywater could reduce urban water
consumption by an annual 140 million cubic meters by 2050 (around 10%), as well
as reduce electricity usage by 560 gigawatthours (about 0.5%) by that time,
according to Gross.
Meanwhile, the country would be able to eliminate the
need of one large desalination plant, reduce carbon dioxide emissions by about
an annual 6 to 8 tons and save about $3 billion-$4b. in direct costs by that
same year, he added.
“Even in a single-house operation, water reuse can
be economical and it can increase water savings by 40%,” Gross said. “It is
recommended that the Israeli authorities will firmly advance and adopt current
initiations for greywater reuse.”