GreenBuild Blog
Monday, July 05, 2010
Finding the Payoff in Rainwater Harvesting
At the LEED Silver-certified Tacoma, WA, police vehicle maintenance facility, two 4,800-gallon culvert tanks collect rainwater and recycle it for toilet flushing. Courtesy of TCF Architecture, Tacoma.
Target Field, the new home of the Minnesota Twins, features an advanced rainwater harvesting and reuse system, the largest to date in professional
sports. Courtesy Wayne Kryduba.
The problem lies often in cost-benefit analysis of rainwater collection systems compared to most potable water prices, which are still quite cheap in the U.S. Using a ten-year cost analysis for a rainy U.S. climate, the rainwater collected over the ten years would cost approximately $4.55 per hundred cubic feet (CCF), which is higher than average water rates in most U.S. cities (but not necessarily higher than the highest-tier rates). The system wouldn’t quite pay for itself just with water savings because the added cost of extra plumbing to convey the water to the points of use hampers overall cost-effectiveness.
Although first-costs are higher than conventional systems, in new buildings rainwater collection systems could potentially eliminate expensive charges for storm-drain hookups, putting an owner “money ahead from Day One,” where the costs of savings are greater than the installation cost. In one project in which I was involved, just the cost of installing the storm drainage pipes to take water off the site and to connect to the town’s storm drains was greater than the cost of installing two 20,000-gallon tanks to hold runoff from the 100-year rainfall event and providing a treatment system that generates enough water for toilet flushing for a good part of the year. In addition, the use was for an academic building whose use pattern just about matched perfectly the annual rainfall cycle of the West Coast.
If seasonal and annual rainfall continues to be more erratic, water rationing and higher prices will be likely, making rainwater harvesting a rational economic response especially for large users. I harvest a few thousand gallons a year of rainwater at my house in southern Arizona, and I can tell you that nothing could be easier (or more sustainably satisfying) than using recycled rainwater for plant irrigation in a dry climate.
Posted by Jerry on 07/05/2010 at 03:49 PM
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Green Building News • Water Efficiency • PermalinkFriday, July 02, 2010
Sewer Mining: Extreme Measure or Viable Solution?
6-Star Green Star-rated building, Council House 2 in Melbourne, Australia, pioneered an urban innovation, “sewer mining” of blackwater for treatment and reuse in buildings. Courtesy of the City of Melbourne.
A 9-story public office building, Council House Two (CH2) in Melbourne, Australia, implemented sewer mining with an in-house blackwater treatment system. Sewage extracted or “mined” from a sewer main located in the street near the building, along with wastewater produced in the building, is purified using a multi-water reuse (MRW) plant in the basement. The wastewater undergoes a micron-sized prescreening, ceramic ultra-filtration and finally reverse osmosis, which together purify it to a Grade-A drinking-water-quality standard.
The system processes more than 26,000 gallons of wastewater per day, and the effluent provides recycled wastewater for toilet flushing, a roof garden and other uses. The sewage treatment plant, coupled with a 5,280-gallon rainwater and fire-sprinkler-test water collection and storage tank onsite, supply 100 percent of CH2’s non-potable water.
There is plenty of water flowing in cities in the sanitary sewer system, so why not tap into it? Considering the increase in droughts, potential water supply shortages and the expense associated with transporting and treating water, sewer mining is an approach that could supplement current water supplies and help prevent a future urban water crisis. In fact, my engineering friends tell me that many new large office projects in Australia are incorporating sewer mining into their design as a viable approach to meeting water demands, especially from cooling tower make-up water.
Posted by Jerry on 07/02/2010 at 11:09 AM
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Green Building News • Water Efficiency • PermalinkOcean Water Desalination: Our Next Source of Drinking Water?
The Tampa Bay Desalination Plant produces 25 million gallons per day of fresh water from seawater using 9,600 of these reverse osmosis membranes. Courtesy of Poseidon Resources.
The $350-million Carlsbad desalination plant near San Diego, California, broke ground late in 2009. Courtesy of Poseidon Resources.
The U.S. is already produces 1.6 billions gallons of water a day from desalination. The country’s largest desalination plant in Tampa Bay, Florida began operations in December 2007 and produces 25 million gallons per day. The plant’s developer has two additional desalination plants under development in California. In San Diego, the regional water authority is planning to supply 10 percent of the region’s total water supply requirements through local seawater and brackish groundwater desalination by 2020.
There are two basic ways to remove the salt from seawater: either distill it as steam from brine or separate the salts from the freshwater through a reverse osmosis or electrical process. In a desalination process, salt water is separated into two parts: one that has a low concentration of salt, essentially drinkable, and the other with a much higher concentration than the original feed water, usually referred to simply as “concentrate.”
At about $900 to $1,100 per acre-foot (one foot of water covering one acre of land, equivalent to about 326,000 gallons), costs for desalinated water are 30 percent or more than conventional sources in California, and the electricity to produce 1,000 gallons costs about $1.10. Given those figures, it’s far cheaper to conserve water than to provide new supply. Conservation and efficiency are always going to be cheaper than new infrastructure solutions.
Although building new desalination plants should be a last alternative for solving urban water supply needs, I think desalination will be part of our 21st-century water future because it’s one of our few drought-proof resources.
Learn more about desalination in Chapter 13 of my new book, Dry Run: Preventing the Next Urban Water Crisis, published in June 2010 by New Society Publishers.
Posted by Jerry on 07/02/2010 at 10:57 AM
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Green Building News • Water Efficiency • PermalinkTuesday, June 29, 2010
Nega-gallons and Aqua-vores: New Approaches to Water Conservation
Swedish architect (and “aquavore”) Anders Nyquist designed this apartment block of 32 units around a central interior courtyard in Nydala, Umea, Sweden. Built in 2006 and illustrating his “split box” concept, there is no connection to the sewer or district heating system, since the water and energy cycles are completely integrated with the building design. Courtesy of Anders Nyquist.
The same is true for water. It’s far cheaper to conserve water than to provide for new supply. Nega-gallons is a new measure of water doesn’t have to be provided as a result of conservation and efficiency measures. Supplying nega-gallons (of demand reduction) is always going to be cheaper than new infrastructure solutions (to increase water supply). In San Diego, for example, the county water agency is relying heavily on nega-gallons in future water supply planning. Owing to investments in efficiency and consumer education, the county is expecting the contribution of water conservation and recycled water (nega-gallons) to increase from 11 percent of total supply in 2008 to 17 percent in 2020.
If water is priced more expensively, people will try to conserve it, by purchasing more water-efficient appliances and fixtures, fixing leaks, using drip irrigation instead of sprinklers, recovering and reusing rainwater and graywater and finding alternatives such as xeriscaping (landscaping with low water-using plants). In this way, each gallon conserved adds a gallon to the nega-gallon supply.
People are especially concerned about water shortages and adverse to paying increasing prices for imported water or more exotic supply sources such as desalination. For this reason, I find that many people want to become “aqua-vores”—only using water that falls on or near their property. While perhaps a bit extreme in today’s world, supplementing public water supply by using rainwater and graywater for non-potable requirements reduces the demand on conventional water sources and thus contributes to the nega-gallon supply.
In deciding to get some or all their water from onsite sources such as rainwater harvesting and graywater recycling than from the public water supply system, aquavores take the equivalent action of “locavores,” who want to eat food grown locally rather than shipped in from 1000 or more miles away.
Posted by Jerry on 06/29/2010 at 01:37 PM
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