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A Path to Net-Zero Water
Water harvesting is no different than renewable energy – opportunities abound in your building to capture a free resource and turn it into an economical solution. The key is to have the right systems in place.
But what if the only water you could use had to be collected solely from rainstorms and recycled from your restrooms? Would your water habits change if you were responsible for treating all of your sewer excess?
A net-zero water building is an innovative strategy that pushes your building to be fully responsible for generating its potable water needs and treating all discharge waste.
“Net-zero water turns your property into a self-sufficient water resource,” explains Amanda Sturgeon, vice president of the Living Building Challenge. “On the supply side, all of your water must be either harvested on-site or sourced from a closed-loop system. For discharge, no water leaves your project site through city pipes – all waste water is treated and reused or infiltrated within your property. Net-zero water means you’re living within your means of what your site can both provide and clean.”
It sounds like an extreme approach, yet aging infrastructure costs may push more and more responsibility on facility managers to meet their own water demands. The Bullitt Center is one of the first buildings in the U.S. to pursue net-zero water.
While net-zero water is technologically feasible for existing buildings, costs are another matter, as are square footage limitations and code complications. This approach is best suited for new construction, where space can be set aside from the onset for storage tanks, additional piping, and filtration systems.
FMs in existing buildings can nonetheless steer their facilities toward water independence with a host of conservation strategies that capture, process, and recycle this natural resource. Improve your bottom line and your sustainability commitments with these five strategies that reclaim greywater and stormwater.
1) Manage with Meters
Water meters are just as critical as energy meters to understanding your consumption habits. While your main utility meter reports how many total gallons are used, it doesn’t break down loads among occupant, mechanical, and irrigation needs. A typical building may consume equal volumes between these areas, but pool areas, dining facilities, or laundry machines are major variables.
You can expand your submetering to virtually any space or system that consumes water on your property, recommends the EPA. These can include individual tenant spaces, cooling towers, HVAC systems, steam boilers, irrigation, water features, pools, and industrial processes.
“Once you have metering in place, you can understand what your systems are doing at any given moment, trend this data, and make adjustments accordingly,” notes Jeffrey Kling, a mechanical engineer with Gibbens Drake Scott, an MEP design firm.
As with any improvement project, you need to capture a before and after picture. This type of granular usage data will help you determine the feasibility of different systems, model diversion rates, and verify savings.
This information may direct whether you want to focus on a harvesting solution like greywater capture or a conservation measure such as faucet aerators. It may seem like a given to focus on low-flow fixtures, but if your irrigation needs are your largest consumer of water, you could see greater returns by focusing on rainwater harvesting.
Leaks can also represent a huge source of water waste within a building, yet without metering they can be hard to detect, according to WaterSense, a product labeling program offered by the EPA. A sweating toilet may seem like a low priority, but a unit that’s leaking 0.5 gallons per minute could add up to over 21,500 gallons a month. Using an average rate of $8.25 per 1,000 gallons of water, that’s over $2,000 a year for a single malfunctioning toilet.
Any harvesting system should also have meters – it’s imperative to know how much water you can viably collect, treat, and recycle. As with renewable energy, your water “generation” is typically dependent on weather events, seasonal demands, and in the case of greywater, occupant habits.
The same fluctuations also impact when and where you can distribute treated water. Irrigation and cooling demands are likely higher during certain months, whereas flushing volumes probably maintain constant levels. These potential end uses for recycled water will impact your collection and storage methods, as well as dictate filtration requirements. Metering data can help you navigate these nuances. PageBreak
2) Collect Condensate
Condensate and blowdown collection is a frequently overlooked yet relatively straightforward harvesting strategy. Water consumed by building and mechanical equipment accounts for up to 30% of water use at an office facility, 20% for hospitals, and 10% for schools and hotels, according to the EPA. Common systems that use water as a heat transfer medium include single-pass cooling, chilled water systems, cooling towers, and boiler and steam systems.
“During the summer months, cooling and dehumidifying produces a significant amount of condensate. You might see columns of water coming from the air handlers, which is generally discharging into the sewer,” says Kling. “Aside from some biologics that could be growing on the cooling coils and any residual metals, this moisture is relatively benign and requires minimal treatment to reuse.”
Depending on the size of your facility and equipment, condensate can generate hundreds of gallons of water each day. Based on ASHRAE data, you can anticipate 0.1-0.3 gallons of condensate per ton of air conditioning for each hour your cooling system operates. A recovery system can harvest 5-15% of your total required makeup water.
You can also take advantage of humidification flow. “Humidifiers might deliver 80% of the water into the air stream. You can capture the 20% that bled off, which conveniently discharges into the same collection pan as the cold condensate,” Kling explains.
To recycle this water source back into your cooling systems, you will need to add a new cement slab, collection tank, and pumps. These can add 3-5% to the total costs of a new system and slightly higher for retrofit applications, according to ASHRAE modeling. Costs will also increase if the water is redirected to landscaping, which requires treatment and larger holding tanks for long-term storage.
3) Save Stormwater
Whether you pay stormwater fees or not, rainwater capture is becoming more common around the nation. Buildings with a large roof area – data centers, big box retailers, warehouses, hotels, and schools – can be ideal sites to collect rainwater, notes Kling, but even dense urban areas and high-rise buildings can add rainwater cisterns. One Bryant Park, a landmark skyscraper in New York City, can capture and store up to 35,000 gallons of rainwater at a time.
Rainwater is typically conveyed from the roof through gutters into storage tanks. Light filtration produces water for irrigation and flushing, though additional sanitization can be implemented to bring it up to drinkable standards. Because the water is cleaned before use, you don’t need to worry about it leaving residue in toilet bowls or containing harmful pollutants for plants.
Take note that water rights laws, which specify ownership of rainwater, vary drastically depending on your region. Some areas have few regulations, others focus on filtration standards, and not every area permits rainwater to be recycled as drinking water. Some even view rainwater as state property and won’t allow it to be collected by private enterprises. Many of these regulations are being challenged, so review your city’s stipulations carefully.
4) Gather Greywater
Greywater offers a way to repurpose discarded water from restroom faucets, showers, and laundry machines. This is water you already paid for, so why not intercept it for a second use?
To harvest greywater, you must have separate piping to avoid the risk of cross-contamination (greywater is generally not allowed to be reused as drinking water). You not only need to connect the collection sites to the treatment tanks, but supply an additional network to pump and distribute the treated water.
You must also include storage tanks that can hold several thousand gallons and a filtration system, which may include copper-silver ionization, UV light, ozone, or chlorine. This technique is ideal for new construction, as the cost of adding new piping to an existing building can be costly. PageBreak
5) Fill Up with Fire Sprinklers
You never know when it’s going to rain, but you know when your fire sprinkler tests are scheduled.
Diverting water released from a fire system test may seem like an unusual strategy until you start crunching the numbers, says Kling. The flow rate for a single test is massive – 250 gallons per minute during a typical 15-minute test. That’s 15,000 gallons for one pipe to be tested four times a year. Now multiply this by the number of existing stand pipes. What you have is a volume of discharge water that equals a significant rain event.
To capture this water, you need a holding tank, which is typically buried below ground to maintain aesthetics or hidden in the basement if you have the space. Because the water has been sitting stagnant in the pipes for several months, it requires particulate filtration. Test water may be used for irrigation or other purposes as it can be planned for capture, stored for long periods of time, and siphoned during periods of need.
6) The Big Picture
“People generally take water for granted,” observes Denis Hayes, coordinator of the first Earth Day and president of the Bullitt Foundation, a civic organization focused on urban ecology. “When faced with low rates and a seemingly abundant supply, there can be little motivation to conserve. But this is an attitude that we desperately need to reverse.”
Water conservation isn’t just a matter of reducing your utility bills – water shortages are a growing issue around the country. Projections indicate that some of our largest cities could be facing water scarcity in the next decade. Record droughts are already giving rise to an increasing number of water restrictions, particularly as many areas are faced with population growth that’s quickly outpacing their water processing capacity.
“On a national level, we forget that water treatment is a highly energy intensive process to extract, treat, distribute, and discharge water,” Sturgeon points out. According to various national data, it takes anywhere from 0.25-3 kWh per 1,000 gallons of water to achieve potable standards. Considering that the U.S. consumes over 400 million gallons a day, clean water carries a hefty energy profile.
To compound the problem, the vast majority of U.S. water infrastructure is in dire need of replacement – the condition of our aging pipes earned a D+ from the American Society of Civil Engineers. This backlog of deferred maintenance and inadequate capacity has become a costly problem.
80% of sewer pipes reaching the end of their life, the American Water Works Association (AWWA) estimates that fixing 800,000 miles of pipes would require a $298 billion investment. The majority of our water main breaks also needs to be replaced, a potential $1 trillion improvement cost. Given that local and state governments are largely responsible for these capital improvements, those costs are eventually passed along to building owners.
Apply the same approach to water conservation as you take with energy – decrease demand and improve efficiency – and any reclamation and reduction efforts you implement will have a tangible impact on your utility bill and community at large.
Jennie Morton firstname.lastname@example.org is associate editor of BUILDINGS.