A Path to Net-Zero Water

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.

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