Commercial buildings are made up of many systems that rely on water. With today’s desire to design green systems, the engineer’s goal has become not only to provide a functional design, but also to keep usage and energy savings in mind. With or without the need to achieve Building Council LEED points, water conservation can be incorporated into a design, even if it is just at the fixture level. Providing a system that reduces water usage will not only lower energy costs, it will also ensure future availability of resources and convey a corporate message that the environment matters.

For the purposes of this article, we are categorizing commercial buildings as office buildings, hospitality, institutional, sports complexes, and retail. Some of the solutions presented also apply to single- and multi-family residential buildings, but they are not the focus of this article, since we want this article to be applied to engineers working in an industry where he/she can apply these tips. Additionally, the article does not directly reference water usage costs because the costs vary significantly around the country.

Low-flow plumbing fixtures

Many breakthroughs have been made in building water systems. These results have led to the replacement of large water-consuming fixtures with low-flow water fixtures. Aerators for faucets, reduced-flow shower heads, and high-efficiency toilet and urinal flush valves are available with an initial capital investment; they often pay back the investment in less than a year, especially when they are used often. Low-flow fixtures in themselves are not a remedy as they don’t save you water if you are filling a pot, getting a glass of water, or doing other things that require a fixed volume of water. They do, however, save a significant amount of water when the number of usages is held constant.

In 1992, the National Energy Policy Act mandated the use of water-conserving plumbing fixtures. Since the law’s inception, low-flow plumbing fixtures—including flush valves for water closets, urinals, faucet aerators, and showerheads—have been further developed to save substantial amounts of water compared to conventional fixtures while providing the same utility through design features such as improved bowl, aerator, and flush valve design. Payback is not addressed here because water rates vary widely across the United States. Although no one is specifying the pre-1992 fixtures, the percentage of pre-1992 fixtures in existing commercial building stock is fairly significant, though specific data to quantify this is hard to come by.

Rainwater harvesting

Commercial rainwater harvesting systems can be a viable option for owners and designers where a building with a large roof area also requires a high demand for nonpotable water. Again, this is based on the AHJ’s guidelines.

Capturing and storing rainwater is an easy and effective way to conserve water through a commercially viable payback period. Obviously, in areas where rainfall is more prevalent, it is easier to capture and store rainwater for meeting demands, thus providing payback of investment much earlier than in areas that have limited rainfall. With a design and components that are simple and a system that is generally easy to operate, upfront and operating costs can be an attractive proposition to the owner. A payback study can be accomplished by defining an area’s annual rainfall and using the availability to compare demand savings based upon local water costs versus system upfront costs.

The demands for a system of this type lie with irrigation and cooling tower makeup loads as the primary considerations behind implementing this method of water conservation. Therefore, the on-site requirements and performance of the storage components should be designed to meet the demand needs of the target load. Other uses of stored rainwater include laundry, toilet and urinal flushing, car washing, and ornamental water features.

Selecting a rainwater harvesting system is dependent on the collection area of the commercial site and the intensity of rainfall in the particular region of the country. Once the availability and demand are calculated, the system should be designed to meet the daily demand throughout the dry season. The system tank should be sized to be filled during conventional rain events with an overflow connected to the stormwater draining system. Additionally, the system should have a connection to the potable water system, through a break tank or some other form of physical air gap, to provide a supplemental water source during periods of low precipitation.

Pressure reduction

In many high-rise and commercial settings, domestic water booster pumps are necessary to overcome the loss of pressure due to increases in elevation and to maintain water supply in water towers and supply tanks. With these higher pressures, water flows through the system with resulting greater flow through terminal fixtures beyond rated flow capacities, and this additional water is wasted as it serves no additional benefit to the rated performance.

Most plumbing codes require pressure-reducing valves on systems where pressures exceed 80 psi. In most cases, these pressures could be lowered by the implementation of additional pressure-reducing valves. Additionally, the higher pressures can rupture pipes and damage fixtures. This leads to even greater waste in the domestic water system. When it comes to the domestic heating plant, if less water flows through the system, then less energy is needed to heat the domestic hot water in the first place.

Leak proofing/leak repair

Leaking pipes can go unnoticed, sometimes for years. Water distribution piping is inevitably installed in every nook and cranny, crawlspace, and chases throughout all types of buildings. Pipes are concealed out of sight, and more times than not, leaks are not found until water damage is evident on chase walls and ceilings.

Rates of water loss vary significantly depending on the type and severity of the leak. Dripping water taps and leakage from toilet cisterns can lose gallons of water per day. Proper preventive maintenance, proactive approaches, and quick fixes are necessary for water conservation, but there are steps that can be taken prior to installation that can potentially discover future leaks prior to the inevitable failure.

Cooling tower water recovery

Cooling towers remove heat from a building’s air conditioning system by evaporating some of the condenser water. Since all cooling towers continually lose water through evaporation, drift, and blowdown, they can consume a significant percentage of a building’s total water usage. Towers that are in good condition, operated properly, and well maintained allow chillers to operate at peak efficiency. Some cooling towers can use recycled water like stormwater or grey water if the concentration ratio is maintained conservatively low. Similarly, blowdown water may be reused elsewhere on-site.

In an attempt to reduce water usage at cooling towers, the designer should focus on the two factors that can be controlled: drift (water droplets that are carried out of the cooling tower with the exhaust air) and blowdown (the removal of circulating water to maintain the amount of dissolved solids and other impurities at and acceptable level designated by the electrical conductivity of the water).

Evaporation is integral to a cooling tower performance and cannot be reduced without an acceptable reduction in performance. Reducing blowdown to the minimum level consistent with good operating practice can conserve significant volumes of water. Treating the condenser water by chemical means usually reduces water loss. Installing conductivity meters on blowdown lines helps reduce water usage during the bleed/feed cycles. Drift can be reduced by baffles or drift eliminators. Not only do these devices reduce water loss from the system, they inherently contain water treatment chemicals within the system to improve operating efficiency and reduce environmental impacts.