Rainwater harvesting,

June 20, 2008 4:13 PM PDT
Rainwater harvesting advocates bring filter tech to the U.S.
by Hanna Sistek 2 comments
SPICEWOOD SPRINGS, Texas--When Joe Wheeler built his new house here in 2001, he was told that it would cost $10,000 to drill a well, and that he wouldn't be able to drink or bathe in the water. Undaunted, he turned to the old-fashioned idea of rainwater collection to solve his water problem.

Wheeler talked to people who had experience with rainwater collection, and eventually installed what was available on the market at that time, so-called first-flush technology. The first-flush system he had installed sent the first, dirty batch of water from the roof into a diverter tube, and collected the rest in a tank. But he soon started questioning the efficiency.

"I don't think it's a valid idea to take 10 percent of the water off your roof and then assume that the rest of the water is fine. Just think about how long it takes to clean up your windscreen from whatever the birds leave on it," Wheeler continued.

Wheeler browsed around on the Internet and found WISY, a German rainwater filter manufacturer. Apart from buying a set himself, he became the company's first U.S. distributor.

How the WISY system works.

(Credit: Rainfilters of Texas)

How WISY works
Under the WISY system, which Wheeler distributes under the name Rainfilters of Texas, the gross filter first gets rid of the initial batch of water and all larger particles in it.


The first of the four WISY filters removes the larger particles.

(Credit: Hanna Sistek)
Then, the water flows to a calming inlet in the storage tank. In the third step, water is pumped back from the tank through a floating suction filter, avoiding sucking up the bottom tank water where bacteria accumulates. Last but not least, a surface-skimming tube on the tank gets rid of particles floating on top.


WISY system's floating suction filters

(Credit: Hanna Sistek)Once pumped up from the storage tank, Wheeler's water runs through two filters (the blue ones in the photo) and finally the last germs are eliminated with UV light (the metallic cylinder in the photo). This makes the water safe enough to drink.


WISY system's surface skimming tube

(Credit: Hanna Sistek)Wheeler's sewage water goes through two barrels. In the first one, all the feces is collected and is broken down by bacteria. After passing another barrel, the residual water flows into a low-pressure-dose septic tank, which is buried in the ground and never needs to be emptied. Most of the water evaporates from the tank, Wheeler said.

The cost of WISY's rainwater collection system depends on the size of the tank, but it can range from $4,000 to $10,000 or more, plus labor. Filters cost around $300, a pump $500 to $800, and the UV light sterilization $1,200 to $2,000. The tank cost around $1,000.

Maintaining the system costs about $250 a year for new UV bulbs and filter cartridges, Wheeler said.

Cost-savings
There is money to saved here: the fee to hook up a new house to the community water grid can be as much, or more, as buying a rain harvesting system. In California, for example, it costs $4,000 to $20,000 to get connected to the grid, according to Jim English, client services manager at Black and Veatch, an engineering firm that conducts water-rate studies. The monthly fees differ between water agencies and range between about $12 and $70, but are generally $25 to $35, or $300 to $420 annually.


To get drinking quality, the water is run through the two blue filters and finally through the UV light sterilizer.

(Credit: Hanna Sistek)Wheeler's company is not the only one in this space. Stark Environmental, a small Columbia, Pa.-based company, is also importing German rainwater filter solutions from a manufacturer called 3P Technik. Stark Environmental's solutions are similar to WISY's, but the filters are made out of polyethylene rather than stainless steel. The price tag of a 3P Technik 1,700-gallon filter system excluding a UV light sterilizer, is in the range of $5,000 to $7,000.

Rainwater collection may get a boost from new storm water guidelines mandated by the U.S. Environment Protection Agency. The so-called MS4 program (Municipal Separate Storm Sewage System) addresses the earth disturbance caused by construction projects. When a new warehouse is built, for example, the amount of soil able to absorb large water masses in the area decreases. In order to diminish the erosion and transfer of sediment that heavy rainfall may cause, MS4 guidelines require municipalities to arrange systems for dealing with the water.

The man behind Stark Environmental, Michael Stark, noted that lately municipalities' focus has changed from simply getting rid of the water to reusing it. With climate change and increasing water shortages, rainwater is an excellent source for irrigation, toilet flushing, and clothes washing, he said. In the case of irrigation, it is even preferable to chlorinated tap water.

"The chlorine kills the bacteria. But in soil there is both good and bad bacteria, and to kill the good bacteria will not help in landscaping," said Stark. Both he and Wheeler believe it is a waste of energy to treat all water up to drinking standards.

"Compare it to how people are hooked on bottled water. How many of them would buy bottled water in the store, just to flush it down the toilet?" Stark asked.

The U.S. is not the only country where rainwater harvesting is heading toward a renaissance. Indian farmers, for instance in the northern state of Punjab, used to be good at rainwater harvesting until they were given free pumps and electricity by populist politicians. Now, with the ground water level sinking--thereby increasing the levels of arsenic in the water--and temperatures rising, non-governmental organizaitons like SIDA, the Swedish International Development Agency, are running programs to encourage farmers to resume their old water collecting habits