NET-ZERO WATER USE IN HIGH-RISE BUILDINGS: A Study in How to Achieve It and Make Money Doing So

NET-ZERO WATER USE IN HIGH-RISE BUILDINGS: A Study in How to Achieve It and Make Money Doing So


The climate today is tough, particularly in the western U.S. where the drought is ravaging the environment and mandating water restrictions. California has particularly been hit hard, with more than 97% of the state affected, and 46% of the state still at exceptionaldrought levels according to the NOAA.

How do we combat this? In a phrase: Net-zero water use. Buildings in the United States use roughly 47 billion gallons of water per day this represents 12% of all water use each day. Fortunately, there are high performance building strategies that can be leveraged to achieve net-zero water use in high-rise buildings, allowing for the reuse of wastewater in an environmentally-friendly and financially-beneficial manner. Net-zero water use ensures that a building never uses more water than it produces.

Lets take a look at how net-zero water use can be achieved through water use reduction and water generation strategies, and how it all can affect your bottom line.

Water Reduction

With the average office building utilizing 12 gallons of water per square foot each year, there is much to be done that can contribute to smart water reduction. Reduction can be achieved through smart plumbing fixture selection, efficient heating and cooling equipment specification, and low-water use irrigation strategies. Lets glance at each.

Restrooms Water savings can be achieved in restrooms through simple off-the-shelf plumbing fixture installations. Altering the flow rate of restroom appliances can greatly save water; in fact, you can achieve approximately 40% water savings over what the plumbing code mandates by leveraging fixture flow rates on urinals, toilets, sinks, and faucets, often with the aid of a water-restricting aerator.

Heating and cooling Cooling tower water loss is the leading culprit behind high water usage in high-rise office buildings. Fortunately, cooling tower water cycles can be increased in order to effectively decrease water usage by approximately 20%. Also, an additional 20% reduction can be achieved by using more efficient cooling equipment in tandem with air-side economizers to reduce the overall need for cooling tower cooling.

Irrigation Incredibly, water savings through smarter, greener irrigation efforts can approach 80% without the need for many costly new pieces of equipment. The utilization of drought-tolerant plants, which is becoming increasingly popular in western states for office parks and homeowners alike, can contribute to most irrigation savings. Additional water savings can be realized through moisture-sensing irrigation controllers and drip irrigation.

Water Generation Strategies

Enormous strides toward net-zero water use in high-rise buildings can also be made through smart water generation strategies. Green building consulting teaches us that such generation can be intelligently performed through the combination of rainwater collection and a blackwater system.

Rainwater collection and reuse system Large buildings have an impressive ability to collect rainwater. A rainwater collection and reuse system efficiently captures, stores, and treats (if necessary) rainwater that falls around the grounds of high-rise buildings. This rainwater is then reused. While such a rainwater collection system can be utilized independently, it can also be combined with a blackwater reuse system for maximum effect.

Blackwater reuse system Two terms to understand when contemplating a blackwater reuse system: Blackwater and greywater. Blackwater represents all the waste water in a building generated from urinals, toilets and kitchen sinksGreywater represents all the other waste water generated by the rest of a building’s equipment.

A blackwater reuse system captures all on-site blackwater and greywater, treats it, and then reuses the water as cooling tower makeup water and toilet/urinal water. Also, a blackwater reuse system can be combined with sewer mining to achieve true net-zero water use. Sewer mining is a high-performance building strategy that allows for the collection of city sewer water from the local mains, and the resulting treatment of that sewer water within the buildings blackwater system. This strategy provides additional water for re-use at the high-rise office building in question.


So, heres the big question: After all this green building consulting and the application of all these high performance building strategies, how does it affect your bottom line?

Pretty well, actually. Estimates for the total price of all the aforementioned strategies sit at about $2.4 million. However, annual water savings as a result of these strategies are estimated to be 12 million gallons a year. When the average United States water cost is applied, this results in $140,000 in savings each year, making the entire enterprise cash-flow positive in just 11 years (factoring in annual water cost escalation of 9%). After that point, the value simply adds up each year.

Currently, an office tower in San Francisco is under construction using these net-zero water use strategies, proving the viability of the concept. And in todays water-challenged times, the demand for more such buildings is at an all-time high. Will your enterprise be the next success story?