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Drinking Water

Treatment for rainwater catchment

October 13, 2010
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If point-of-use/point-of-entry (POU/POE) water treatment in North America is seen as a “maturing” industry by some, there’s one POU/POE market segment that looks like an adolescent starting a growth spurt. It’s treatment of harvested rainwater.

Behind it are several phenomena: drought, watering bans, a new “green” consciousness among consumers, among others. The idea of using rainwater for homes and businesses is catching on fast, even in moist climates.

“It’s just sort of exploded in the last year or two,” says Dennis J. Lye, Ph.D., outgoing vice president of the American Rainwater Catchment Systems Association (ARCSA), based in Austin, TX, a trade group for system installers, manufacturers, consultants and individuals working in the field.

A research microbiologist for the US Environmental Protection Agency’s regional office in Cincinnati, OH, Lye cautions that his views on rainwater catchment are his own and don’t represent the views of EPA. But as part of teaching and research he has done for years, he has visited many home rainwater systems in northern Kentucky, Ohio and West Virginia.

Many people in that region use rainwater as a source of potable water because underground karst formations tend to make well water brackish. In many other parts of North America as well, “There certainly is a demand for it,” he says.

Brian Soderholm, product manager with Water Control Corp., based in Ramsey, MN, agrees with that view.

“There’s a lot of buzz about it,” says Soderholm, whose company installs treatment systems for commercial rainwater users.

Rainwater is also being noticed now by some major manufacturers involved in water treatment. For instance, Watts Water Technologies, Inc. is promoting rainwater harvesting equipment, seeing business opportunities in it for dealers.

ARCSA’s membership, now over 500, has nearly doubled in the past year. Interest also has grown recently in the research community, with more rainwater research turning up in scientific journals, Lye says.

Is the water safe?

For years, irrigation from a “rain barrel” or cistern was a familiar use for rainwater. Now, more people are looking at rainwater as a potable water source. Lye says that due to the current search for more “green” building solutions, the number of inquiries from consumers about rainwater systems is now about equally divided between those interested in potable water and others looking into irrigation.

“The first thing they’re concerned about is the quantity, and they usually have to end up supplementing it to some extent” from a well, public water or a water hauler, Lye says. That’s especially true for a rainwater system that will be used for irrigation.

For that reason, Mark Illian discourages rainwater for irrigation. He’s founder of the Center for Rainwater Harvesting (CRH), the for-profit offshoot of a Houston, TX-based non-profit organization, Nature Healing Nature. The latter installs low-tech rainwater systems for drinking in poor countries and teaches other non-governmental organizations (NGOs) about it. In North America, CRH sells and installs residential and other rainwater systems.

“I tell people that when you say irrigation, your price for installation of the much larger storage system required for that goes up exponentially,” Illian says.

For those seeking potable water from the rain, the next question is: “Is my water safe?” That’s where the water treatment professional can profitably enter the picture.“The potable part is the trickier part,” Lye says.

Leaves go first

Despite rainwater’s idyllic image, it is contaminated when it comes off a roof. “Whatever is on your street or on the ground outside is what’s in your rainwater,” Illian says.

The most common water quality complaint heard by Lye from rainwater system owners is the taste and odor issue. Some have cartridge filters in their systems, but they usually don’t replace them frequently enough.

“The filters always have a microbial load — they do not maintain them the way they should,” Lye says, adding that entire microbial “communities” can grow on rooftops. So the system should first have a leaf or debris excluder to keep out the largest debris such as twigs, leaves and insects.

Between rooftop and cistern, the customer should have some kind of “first flush” or “roof washer” system. Whether manual or automated, these valve systems divert to drain the first few minutes of a rainstorm, containing the most debris.

Illian describes a system of vertical pipes he installs that causes settling of debris such as sand from roof shingles, followed by a designed overflow of clear water into storage. With such systems, “There’s nothing wrong with collecting water from the typical compositional [shingle] roof,” he says.

After storage

As with any other home water system, a standard pressure tank and pump will be essential. In the supply line after the cistern, the first potable-water treatment component should be at least one and, better yet, a series of two or three particle filters of successively decreasing pore size. Lye urges starting at about the 30-micron level and working down to a pore size as small as 1 micron absolute.

After particle filtration will come disinfection.

“Bird droppings are a big culprit” in rainwater, Water Control Corp.’s Soderholm says. “E. coli is a major issue, as is the potential for people getting sick from Crypto, Giardia, Legionella, algae and rodent droppings.”

Lye says chlorination can be used to disinfect rainwater, but notes that consumers tend to prefer non-chemical disinfection such as ultraviolet (UV) or ozone. Chlorination can be used for residual disinfection.

Ultrafiltration also can be used to remove cysts, algae and bacteria. In one recent example with a larger system, GE Water & Process Technologies provided ultrafiltration to the Grove Farm Co. on the Hawaiian island of Kauai. A successor to a sugar plantation, the company is now a private development concern involved in diversified agriculture, community development and environmental conservation.

Grove Farm spokeswoman Marissa Sandblom said the new public water system draws rainwater from a ground collection network and supplies potable water to the local community, to replace declining groundwater supplies. (Parts of the island have some of the highest recorded rainfalls in the world — in excess of 400 inches annually.)

After disinfection, system owners like to have a polishing filter, typically activated carbon, to resolve taste and odor issues and reduce hydrocarbons and other contaminants.

Not your average system

Experts say at least two other technologies found in many conventional water treatment systems are usually not needed or present in rainwater catchment. They are:

  • Softening. Rainwater is naturally soft. Ion exchange softeners also require water for the regeneration cycle which may not be abundant in rainwater storage. However, specialty media can be used to reduce minerals or metals other than hardness.

  • Reverse osmosis (RO). Experts say this technology, while highly effective at contaminant removal, is less desirable for rainwater systems because of the relatively high proportion of water it sends to waste. Of course, some consumers drinking rainwater may still want point-of-use RO as an undersink backstop.

    Lye says dealers working on rainwater systems should also check feedwater pH and alkalinity, because rain in some regions can be acidic and corrode metal pipes. In that case, the dealer will want to recommend pH-raising and/or buffering.

    Dealers also can consider commercial treatment opportunities in rainwater. Soderholm says his company installs assembled skid-mounted systems for rainwater used for cooling tower makeup water, vehicle washes and other non-residential applications.

    “The four elements of any rainwater system are collection, storage, disinfection and delivery. We address the disinfection and delivery parts,” Soderholm says. Water Control Corp.’s systems offer two basic commercial disinfection packages with monitors and controls: ozonation or UV.

Feels good, tastes great

Dealers should be sure that systems delivering potable rainwater comply with local building and plumbing codes. The US Green Building Council has developed its LEED standards for rainwater systems, and ARCSA is in the process of writing its own industry standards. Rainwater industry people urge consumers and installers to look for NSF/ANSI drinking water product certifications.

Two states, Colorado and Washington, prohibit use of water from rainwater catchment. According to Lye, those states take the view that water draining off manmade structures should be returned to natural water supplies. Lye thinks that small rainwater systems in those states are rarely prosecuted, with regulators focused on large “wholesale” catchment. ARCSA is seeking to persuade those states to ease regulations on smaller systems.

On the other side of the coin are states like Texas, which actively encourages property owners to harvest rainwater. As dealers learn the technical ropes of treating harvested rainwater, they shouldn’t lose sight of some of its positive sales points, Illian stresses.

“They should make sure they tell people how wonderful rainwater is for their hair and how very clean and sparkly a flavor it has,” he says. He waxes enthusiastic: “Having a rainwater system is a wonderful way to reconnect with nature. There are fewer contaminants in it than many municipal waters. We shouldn’t be afraid of the rain.”

Recent Articles by Tom Williams, Senior Editor

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