Israeli Science Teacher Invents Low-tech Water Treatment System

Israel is famed for its advanced but costly water technology; Amir Yechieli's system to tap rainwater involves barrels. And gutters.

Rain harvesting system being installed: on the right improvised settling tanks , on the left – what would be clean storage tanks .
Amir Yechieli

Some boast that clever Israeli water technology will save the world. Yet one intriguing Israeli invention is so low-tech that it doesn't even need electricity.

A simple rainwater utilization technique invented by a 63-year-old Jerusalemite science teacher is now flushing toilets at about 140 Israeli schools, three in the U.S. (watch that number rise), and is bringing potable water to schools in Kenya, where Amir Yechieli says the kids don't only drink it during school, they take clean water home in bottles too.

He has a business license, but Yechieli decided in principle not to patent his concept. He hands out blueprints for free and shrugs at royalties for his one-man operation, Yevul Mayim ("Water Harvest"). It's his gift to the world.

"The important thing is for the idea to serve as many people as possible in the world," he told Haaretz. "Patents easily translate into legal wrangles, which would be counterproductive to the world's needs."

What the world needs, says Yechieli, is a cheap, sustainable way to tap rainwater.

Yechieli system installed at  Hayovel elementary school, Jerusalem: Note the heightened, round-bottomed settling tank and series of storage tanks, prettily decorated with trees.
Lauren Sonnenberg

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Yechieli's unpatented patent is a round-bottomed "settling tank" perched on a stand to keep it upright.

Capture the rainwater that falls on the roof – gutters are your friend. (Yechieli adapts the system to the specific roof structure). Channel the water from the gutters to the settling tank.

Let the rainwater with its suspended particles, dust and germs stand in the tank for up to three days, during which almost all the particles suspended in the rainwater will sink to the bottom.

That's the sole force at work: the planet's gravity.

 Encinita farm school (north of San Diego)- recently imported settling tanks from Israel, to utilize rainwater.
Amir Yechieli

After one to three days, the water in the tank is clean and its rounded bottom is coated in sediment. Open a valve at the bottom, release the bottommost 10 liters with the muck.

For the remaining water in the settling tank to be drinkable, it should be passed through 5-micron carbon or charcoal filters, positioned between the settling tank and storage tanks, to remove remaining minerals and most bacteria. The settling tank is opaque so algae cannot form (they need sunlight).

Importantly, the water is stored in the settling tank for no more than two weeks. That is too short a time for bacterial soup to grow from the suspended cells that do remain. Leave the water longer (albeit more than just two weeks), and soup you will get.

"The longer you keep non filtered water in the reservoir, the higher the risk for bacterial multiplication," Yechieli observes, adding that the filters cost very little. "You change them every few months. I give the schools 20 extras to last them five years," Yechieli says.

He also points out that during Israel's rainy season, i.e., winter, storage tanks in Israeli schools will typically fill in a couple of weeks, barring drought. "Typically we fill up the Israeli systems 10 to 20 times per winter," Yechieli says. "In Africa, on the other hand, it's entirely different story – the dry seasons are shorter and the temporal rainfall distribution is much favorable. The water is mostly  used for drinking and therefore is filtered... and filtered rainwater would stay pure for unlimited time, as long as no light penetrates the tanks."

The Yechieli system, installed at the Eden farm school, Emek Hamayanot, Beit She'an, Israel. Note the round-bottom settling tank (leftmost, heightened) followed by a chain of storage tanks. Rainwater collected from the roof can irrigate the greenhouse throughout the winter rainy season, says Yechieli.
Amir Yechieli

In Israel, his settling containers are made by the barrel manufacturing company Hofit. But, like the Israeli cliché, Yechieli is an improviser.

Remote African schools can hardly buy his signature settling tank from Israel, ship it over and so on. When working in Africa (financed by nonprofits Water Works for Girls’ Education and Empowerment and Tag International Development), Yechieli improvises the whole system. "Take a regular tank, insert a diagonal base in one corner, drill a 2-inch pluggable outlet to flush the sediment. It may not be as efficient as a proper settling tank but it's good enough," Yechieli says. He makes it sound very easy.

And frustrating. In Africa, he went to factory owners and offered them his blueprint, for free. They told him that if he paid them to make a mold, they'd make the tanks but otherwise forget it, he says. Thus the need to improvise.

Why bother to clean water for flushing toilets? Even there water clarity is good, Yechieli says. "You can't flush with brown water, it isn't aesthetic," he says. More consequentially: "Over time, dirty water can damage the flushing mechanisms."

Bad zoo

This is the sort of water technology most often associated with Israel: At the IDE and Veolia Sea Water Reverse Osmosis Desalination Plant in Ashkelon.
Eitan Simanor / Alamy Stock Photo

If the water is to be used for sewage, the settling tank can be connected to one or a series of interconnected, lined-up flat-bottom storage containers.  

What about good old cisterns? "Any system based on a single large tank is uncleanable," Yechieli says. "The sediments can't be flushed out  and the water will become contaminated. You wind up with a zoo in there."

Don't the tanks need periodic cleaning? Not his settling tank, Yechieli says. As for the interconnected flat-bottom tanks, disconnect them, lay them down and hose them down once a year, he says. Reconnect and continue.

If the institutions installing his device adhere to his protocol, "step by step, by my written instructions, their water should be perfectly safe,” Yechieli assures.

A small installation—four tanks made by Hofit, a stand and a pump—costs around 15,000 shekels (around $4,000), he says. The cost of improvised systems changes, though he points out that buying guttering costs a fraction of the price of drilling for groundwater, and his water will be cleaner than anything from the ground. And the system doesn't need electricity, which most African villages do not have. All it needs is a road to get the tank to the school, and the man who had the idea.