Water Efficiency (WE) Prerequisites

Prerequisites in LEED are used to set minimum baselines for performance. In the case of water efficiency, three areas are addressed.

• Outdoor Water Use Reduction LEED recognizes that water is often used on building exteriors for things like irrigation of planted materials or lawns. The stated intent of this prerequisite is “to reduce outdoor potable water consumption and preserve no and low-cost potable water resources.” The requirements are to show a basic effort to either eliminate any need for irrigation or to reduce the amount of irrigation needed by at least 30 percent compared to a calculated baseline for the site’s peak watering month. Tactics include selection of plants that need less water and irrigation system efficiency.
• Indoor Water Use Reduction The intent of this prerequisite is to similarly reduce water consumption, but inside the building in this case, and preserve potable water resources. At a minimum, aggregate water consumption must be reduced by 20 percent compared to baseline requirements. Further, all newly installed plumbing fixtures need to be labeled under the EPA “Water Sense” program or a similar applicable program for efficiency.
• Building-Level Water Metering It may be surprising for some to learn that certain areas of the country don’t use or require water meters to be installed in a building. Utility based water usage charges are calculated in a different manner. LEED therefore requires in this prerequisite that a building level water meter is installed to provide the bulk total water usage of the building and related grounds. Further, if the building becomes LEED certified, then the owner agrees to provide the bulk water usage data (monthly and annual) for a five-year period from certification or occupancy.

Once these three prerequisites are satisfied, then earning points through water efficiency credits becomes possible.

Water Efficiency (WE) Credit Opportunities

There are four possible credit categories here–three extend the prerequisite levels of efficiency and one addresses process water use.

• Outdoor Water Use Reduction In order to earn points in this credit, there are similarly two options as in the prerequisite. First, if it can be demonstrated that the landscape does not require a permanent irrigation system beyond a maximum two-year establishment period, then 1-3 points are possible depending on building type. Second, if an irrigation system is used, but it can be demonstrated that the landscape water requirement (LWR) is reduced by at least 50 percent (i.e., more than the minimum prerequisite requirement of 30 percent), then 1 point can be earned. If reductions of 75 or 100 percent are shown, then additional points can be earned up to 3 total.
• Indoor Water Use Reduction In order to earn this credit, additional fixture and fitting water-use reductions compared to the baseline calculation must be demonstrated beyond the 20 percent prerequisite. Essentially, one point is awarded for every additional 5 percent reduction above 20 percent; up to 5 or 6 points for buildings that achieve up to 45 or 50 percent water use reduction. Exemplary performance (potentially eligible for an innovation credit) requires at least a 55 percent reduction. Some building types require some additional equipment documentation for efficiency.
• Optimize Process Water Use The intent behind this credit is to conserve water used for mechanical processes while also controlling corrosion and scale. There are three options to demonstrate performance for this credit, all of which rely on sustainability focused engineering design. The first option is for cooling towers and evaporative condensers based on a one-time potable water analysis in the system compared to five control parameters. In addition, controlling the number of cooling tower cycles and/or using recycled water in the system needs to be addressed. The second option is based on optimizing water use for cooling by comparing actual water use reduction to an engineered baseline. The third option allows the use of recycled alternative water to meet 20 or 30 percent of the water demand for the system. For any of the options selected, 1, 2, or 3 points can be earned depending on the degree of performance and the building type.
• Sub-System Water Metering LEED recognizes that it is difficult to measure your water use, let alone conserve it, if you cannot track it in real time. Relying on the municipal water meter to track water usage is not enough, because it’s a bulk building measure and usually only offers historical data. Therefore, this credit is available for any building design that includes permanent water meters for at least 80 percent of two or more water subsystems as may be applicable to a project. That includes irrigation, indoor plumbing fixtures and fittings, domestic water heaters, boilers, reclaimed water, and other process water. Particularly important for LEED Operations and Management (O+M), it is pointed out that, “Submetering water subsystems helps facility managers track changes in water usage over time and provides the data necessary to identify opportunities for water savings by end use, which may help improve a project’s water performance score. Submetering is a vital component of a successful water management program; metered data enables monitoring of consumption and costs as well as progress reporting throughout the building life cycle.”

Clearly, there is a multifaceted approach in LEED to help achieve water efficiency in buildings and conserve natural water resources.

WATER MONITORING AND METERING SOLUTIONS

To address water efficiency and sustainability goals, determining a baseline water use for a building and its subsystems is the first step. That data can identify the normal or sustainable levels of water usage over time. Reducing water usage by detecting leaks and shutting off unusual flow helps to assure that water is not inadvertently wasted or that other associated problems arise. If a water leak does occur in a building, then someone needs to know about it quickly so that the water flow can be stopped and the problem repaired. There are several common approaches to address this as discussed in the following sections.

Stand-Alone Water Sensors

Simple visual or auditory observation by users or maintenance staff in commercial buildings is the most basic, but obviously the most unreliable, method of detecting a water leak. That is because leaks can happen even when the building is not occupied or when maintenance staff are off duty. Even if the building is occupied, people may not be near the location where the leak occurs (e.g., mechanical rooms, etc.) If the leak is seen, then some people may not recognize it as a problem, assuming that it is a normal maintenance or cleaning activity.