Access to fresh water is one of the world’s major geopolitical issues, yet in most of the U.S. we still use drinking-quality water as if it were free and unlimited. A substantial portion of this usage happens in buildings where leaky plumbing drips it away and fixtures designed decades ago use exorbitant quantities.
In some areas of North America, water is drawn from ground and surface sources at unsustainable rates—in other words, withdrawals from aquifers exceeding annual recharge rates. For much of the year, for example, the Colorado River no longer reaches the Gulf of California. In the U.S., we currently withdraw more than 300 billion gallons of fresh water per day from streams, reservoirs, and wells. Even in places where the water supply has traditionally not been a concern, problems are appearing as populations grow or precipitation patterns change (perhaps due to global climate change).
Toilet flushing uses over 4 billion gallons of water per day in the U.S. alone. While older toilets use about 4 gallons per flush, modern toilets conform to the requirements of the Energy Policy Act of 1992 and use no more than 1.6 gallons per flush (gpf). The Energy Policy Act of 1992 also mandates that showerheads and faucets can use no more than 2.5 gallons per minute (gpm); some models use substantially less. Retrofitting these devices in older buildings is usually a very easy and extremely cost-effective investment.
GreenSpec lists plumbing fixtures, such as low-flow toilets, showerheads, faucets, and waterless urinals, that significantly outperform federal water efficiency standards and meet or exceed EPA’s WaterSense standards. Equipment that can be combined with low-flow fixtures to further save water through refining on off controls is also included.
Energy use of water systems
Constant access to clean hot and cold water is a great creature comfort, but comes at a high cost. Treating and transporting potable water and wastewater is energy and chemically intensive. Heating and cooling water also uses a great deal of energy. Wasting water also wastes energy. Attention to increasing the efficiency and performance on plumbing fixtures, water heaters and coolers, and wastewater options are important elements of green building.
Heat-pump water heaters can be very efficient, but are not a good fit for all environments. On-demand gas water heaters are more efficient than storage-tank type systems. If storage tank-type water heaters are used, consider adding an insulating blanket, which can reduce standby heat loss by 25% to 45% according to the U.S. Department of Energy.
Heat exchangers and heat recovery systems can help optimize the performance of residential and commercial hot water heaters.
Many types of solar thermal systems are available and increasingly used for both water heating and pool heating. These systems are covered in Heating, Ventilating, and Air-Conditioning (HVAC).
Rainwater harvest and graywater recycling
The drain on limited water supplies can also be reduced by harvesting rainwater. On some of the Virgin Islands, rainwater-storing cisterns provide the primary water supply to most homes. In parts of the U.S., it is not uncommon for collected rainwater to be used for landscape irrigation, toilet flushing, laundry and other nonpotable uses in both residential and commercial buildings. For use as potable water, collected rainwater should be filtered and disinfected. Rainwater collection systems are listed in the Utilities category.
Consumption of potable water can also be reduced by recycling graywater for nonpotable uses, such as irrigation and toilet flushing, although these systems may be prohibited by local health codes. In most of California it is legal to use graywater for landscape irrigation, provided the system meets certain conditions.
The other end of the plumbing system is wastewater disposal. Many conventional wastewater treatment systems, including both large municipal systems and private on-site septic systems, are inefficient and/or expensive. Alternative technologies—from composting toilets and recirculating sand filters to ecological wastewater treatment systems that rely on enhanced biological treatment processes—are available for systems of all sizes.
graywater systems and composting toilets can significantly reduce wastewater discharge from buildings, offset irrigation demand (graywater), and treat waste and recover nutrients onsite.
The three major materials currently used in supply piping in North America are copper, chlorinated polyvinyl chloride (CPVC), and cross-linked polyethylene (XLPE or, more commonly, PEX). Polypropylene (PP) piping is also available, though far less common.
Most sanitary drain waste and vent (DWV) piping used today is made from PVC or ABS plastic, replacing cast iron, the traditional DWV pipe material. Vitrified clay pipe can be used in buildings as drain pipe but is more commonly used for larger-diameter sewage applications (where it competes with concrete and PVC); although heavy and labor-intensive, vitrified clay is the most durable waste and sewage piping material. Finally, there are some polyolefin (polyethylene and polypropylene) plastic pipes that can be used for drainage and venting.
All of these materials present their own environmental challenges, and while there are life cycle analysis studies that compare some of these options, there is to date no exhaustive study that addresses the range of relevant issues including manufacturing impacts; potential corrosion and leaching concerns; energy impacts of plumbing design and layout; and end-of-life considerations.