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This HOG Craves Mud, Too—Minus the Dirt

Rainwater HOGs store rainwater simply, unobtrusively, and inexpensively

By Sara Fernández Cendón

At a time when more than half of the United States is experiencing “abnormally dry” conditions, according to the U.S. Drought Monitor, water management has taken on a new urgency. Rather than waiting for large-scale, complex systematic solutions (or for someone else to invent the product of her dreams), Australian architect Sally Dominguez designed a water tank that solves a baffling design quandary with a minimum of building technology: How do you store rainwater unobtrusively in a residential scaled-system that’s simple and affordable?

Birth of the HOG

While working on residential infill projects in inner-city Sydney, Australia, Dominguez had an epiphany. She was interested in exploring rainwater management, but all the products available at the time were designed for rural use. Their scale and shape (wide, round steel tanks with storage capacity sometimes exceeding 1,000 gallons) were nowhere near appropriate for dense urban areas.

Her only option was to use spaces seldom considered valuable: underneath floors, inside walls, along narrow alleys. The problem was how to make flat-walled tanks fit in those spaces. Steel-tank manufacturers refused to create the rectangular tank Dominguez envisioned; they argued the walls of such a tank would bulge with the weight of the water. Dominguez settled on placing a hole in the middle of the containers to keep its walls from bulging—the hole’s circular walls would act as an inside-out brace.

She also knew from prior product-development experience that the manufacturing method known as “rotomolding” (rotational molding) worked well for creating hollow plastics. “And then I thought about Legos,” Dominguez says. “And I thought, ‘Wouldn’t it be cool if this thing were like a module that you could stand on any of its sides and join to the next one, and if water could flow through them without impediment?’”

And thus, the first Rainwater HOG tank was originally manufactured in Australia in 2005—and introduced when rainwater was still considered “gray” water and thus named H2O Grey, or H2OG, or HOG. A version of the tank manufactured in the United States is now available for the U.S. market, which has become the product’s largest, along with growing markets in Singapore and Japan.

HOG Specs

The HOG’s greatest virtue is its flexibility. Designed to support its full weight on any of its sides without bulging (thanks to the clever system of bracing holes), the HOG can be installed vertically or horizontally, and is completely modular. An empty tank weighs about 40 pounds, and a full tank weighs 400 pounds more. Its compact size (20 by 9.5 by 71 inches with a 51-gallon capacity) means it can be easily retrofitted and can also be connected to adjacent tanks for greater capacity. The HOG exists in two versions: one made of recycled plastic, and one from virgin materials. Because potable water cannot be stored in recycled plastic containers, and because water for toilet flushing, too, has to be stored in food-grade containers, the recycled plastic version of the HOG can be used only for irrigation.  

Though the HOG’s design is mostly functional, its low profile and simplicity are big parts of its appeal. Even though it has not been formally advertised, the product has won eight major awards (including selection as a Top-10 Green Product) and received quite a bit of press. Word-of-mouth marketing has aided its ubiquity (you can buy Rainwater HOGs on, as have its clever name and consistent visual identity (including a cute mascot), all designed to attract mainstream consumers. In a field where technological sophistication is often fetishized, the HOG distinguishes itself by showing up with just enough design to do its job and get out of the way, hidden under a deck or in a wall.

At just under $300, the tank has turned out to be attractive to architects, who bring it to their clients’ attention, and to institutions such as schools, that don’t balk at the investment if in return they get longevity and ease of maintenance. Dominguez estimates current annual U.S. sales at about 1,200 tanks.

HOGs in Action

Nundah School in Queensland, Australia, has installed 114 HOGs (custom-made in black and yellow, the school’s colors) for toilet flushing. Collectively, the tanks hold 5,700 gallons of water, and are grouped into color blocks along the exterior wall of the school library, making quite a design statement.

Jeff King, a green-building contractor in San Francisco (where Dominguez and Rainwater HOG are based), used the renovation of his own home to experiment with rainwater management. King designed a system to divert rainwater from more than 75 percent of his total roof area into nine horizontal HOGs installed in the crawlspace of a cellar. The water is then used for flushing two of the home’s toilets. The system is designed to use water collected during winter (California’s rainy season) to flush toilets well into the dry season. After the tanks empty out, the toilets switch over to city water. A backflow-prevention mechanism is in place to keep rainwater from contaminating city water as the two systems converge in the home.

King says he could have used a traditional tank, but to place it in the 3.5-foot-high crawlspace he would have had to install it first, and then build around it. “The water HOGs gave us the flexibility to bring in the tanks at the appropriate time in the job, and they also gave us the flexibility to add to and subtract from the size of the system,” says King. “I knew I could do whatever I wanted to with the HOGs, as opposed to being committed to digging a giant hole for a 450-gallon tank.”

This article is being published for informational purposes only and is not an endorsement by the AIA. The AIA does not approve, sponsor, or endorse any product or material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.


Sally Dominguez, Rainwater HOG’s inventor, stands with a HOG tank in USGBC founder David Gottfried’s backyard. Gottfried has installed nine HOGs in his LEED Platinum home. Image courtesy of Rainwater HOG.

Rainwater HOG 51-gallon tanks can be configured as modular systems to harvest as much or as little rainwater as a site allows. Image courtesy of Rainwater HOG.

Rainwater HOG tanks installed horizontally underneath a deck. Image courtesy of Rainwater HOG.

Rainwater HOG system in a Mill Valley, Calif., spec home designed by Geoff Butler, with 10 vertical HOGs attached to a concrete retaining wall behind the garage. Image courtesy of Geoff Butler.

Rainwater HOG system at Nundah School in Queensland, Australia, where yellow and black HOGs holding 5,700 gallons of water are used for toilet flushing. Image courtesy of Rainwater HOG.


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