Green Plumbing Systems Save Water and Energy

Design the Plumbing System to Save Water and Energy

Efficient plumbing layouts

Green layouts include clustering hot
water uses, optimizing pipe diameters, minimizing run lengths, and reducing bends (particularly hard 90 degree corners). These improvements mean less water and energy are wasted waiting for hot water to reach a distant faucet.

Hot water circulation

Hot water circulation saves water by getting hot water to the point of use with virtually no wait. Some hot water circulation systems save energy, while others increase energy use.

Gray water collection and use

Gray water options
As much as 60% of all residential waste water comes from baths, showers, laundry, and the kitchen. In a household using 100 gal. of water a day, 60 gal. could be diverted from municipal or private sewage treatment and used for another purpose. That amounts to recovering more than 21,000 gal. of water a year in a single household.

Drain water heat recovery systems

Drain water heat recovery can make sense for people that prefer showers to baths. This is a good way of capturing some of the heat in waste water that would otherwise be lost. As much as 90% of the energy used to heat water goes down the drain with it. Drain-water heat-recovery devices are simple to install and cost-effective.



Producing hot water can account for as much as 17% of overall energy consumption at home, according to government estimates.


Composting toilets are very green
In conventional construction, either a municipal sewer hookup or a one-purpose septic system handles both black and gray water. A standard septic system consists of a concrete septic tank where solid waste breaks down and a drain field where liquids percolate into the soil. In areas where drainage is poor or there isn’t enough room for a drain field, an alternative system may be an option. There are many types of alternative septic systems. Composting toilets, which require very small amounts of water or none at all, are another option when a conventional system isn’t practical.

Rainwater collection systems are an obvious way of reducing the strain on public and private water supplies. A simple system consists of a rain barrel filled by a downspout from the roof and used to water the garden and lawn. More complicated systems with large cisterns can supply most of a household's water needs.

Low-flow faucets, toilets and showerheads save energy and water. High efficiency fixtures are important elements of a water conservation strategy. Across the board, plumbing fixtures are far more efficient than they used to be, doing the same job with a lot less water.


LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. EA7 (Energy & Atmosphere) offers 2 points for efficient hot water distribution; WE1 (Water Efficiency) offers 1 point for installation of a gray water system.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Ch. 8 — Water Efficiency: Up to approximately 80 pts. for indoor water consumption (801 & 802); up to 24 pts. for irrigation (801).


Plan ahead to save hassles later

Plumbing systems are complex, expensive, and largely inaccessible when construction is complete. For those reasons, careful planning pays big dividends.

There are two sides to every residential plumbing system: supply and waste. Within those broad categories are a number of subsystems, many of which present opportunities for conserving water, energy, or both.

A well designed plumbing system is capable of saving thousands of gallons of water every year. In many communities, saving water also saves energy because a lot of electricity is used to pump water from source to houses.

With planning, the energy needed to make hot water can be significantly reduced. Solar collectors are one obvious answer, but even in homes with conventional heat sources energy savings can be sizable.


First, buy efficient appliances

Most of the opportunities for energy and water conservation in a plumbing system arise from specifying an efficient water heater, an efficient clothes washer and dishwasher, low-flow showerheads and faucets, and reducing water consumption. But the distribution system itself also has an impact.

Anyone serious about conserving water should start with the low-hanging fruit; that means that the greenest homes do not include a swimming pool. Omitting a swimming pool will also save energy, since pool pumps, filters, and heaters are notorious energy hogs.


Minimize the wait for hot water, cut the cost

Minimizing the amount of hot water that is wasted as homeowners wait for a sink faucet or shower to come up to temperature will save water (and in some cases, energy). If the source of hot water is at the other end of the house, this can quickly add up to thousands of gallons of water needlessly down the drain over the course of a year. If an on-demand water heater can be installed close to a kitchen or bathroom where most of a home's hot water is used, it can partially alleviate this problem.

In all cases, hot water lines should be insulated. Supply lines may run through chilly joist bays or walls on their way to a kitchen or bathroom. In winter, this energy isn’t really thrown away because it makes some contribution to heating the house, but in summer this heat loss is a complete waste that increases cooling loads. Insulating hot water lines is a relatively inexpensive way of reducing the problem and keeping heat where it belongs.

Home-run manifold systems have many advantages. From an energy conservation standpoint, they also have a drawback: they are harder to adapt to hot-water circulation systems. With a trunk-and-branch approach, all hot-water outlets in a bathroom can be served by a single return line and pump. If you get hot water close to the showerhead it will also be close to the sink. In a house with a home-run system, each hot-water line needs its own circulator.

In either case, it pays to design the plumbing system to keep hot water supply lines as short as possible and to make sure they are well insulated. Green building guidelines from the National Association of Homebuilders recommend runs of no more than 30 ft. between the water heater and bathrooms and kitchen.

Stacking bathrooms over one another and moving the hot water heater to a central location in the house are steps that can help.


Consider PEX instead of copper

It wasn’t all that long ago that copper was the top choice among residential plumbers. It’s completely recyclable and, with a few exceptions, a dependable performer. But in some areas of the country, copper is being eclipsed by cross-linked polyethylene (or PEX). PEX tubing is flexible, tough, and suitable for both hot and cold water. PEX lines reduce the risk of leaks and make installation faster and less difficult because, unlike copper, they don’t need elbows to turn corners. Copper is a poorer insulator than PEX, too, so use of the flexible tubing can slightly reduce energy losses on hot-water lines.

The main drawbacks to PEX are that it can’t be recycled and it’s a plastic made from petrochemicals. But there are other factors:

Copper is expensive. Copper tubing is now so pricey that thieves are raiding unoccupied cottages, construction sites, and even underground utilities. PEX tubing can be less expensive than copper tubing, although PEX fittings are usually more expensive than copper fittings.

Acidic water can degrade copper. Staining and even pinhole leaks can develop when water supplies are acidic, a not uncommon problem with private well water and municipal water in some areas. Water acidity won’t affect PEX.

CPVC also is less expensive. Another plastic option is chlorinated polyvinyl chloride (CPVC). It, too, is less expensive than copper and has many of the same advantages as PEX. However, this family of plastics comes with a lot of environmental baggage, mainly health concerns about how the material is manufactured and the potential release of dioxins when it’s incinerated.


Think about separating gray water from black water

Waste water disposal systems present opportunities for both energy and water conservation. It’s easy to dump all liquid waste down the drain and forget about it, and that’s essentially what many urban homeowners are forced to do. They may not have any practical means of separating different types of waste water and handling them accordingly, at least in existing construction. But rural homeowners can find ways to get a second use out of some waste water, and they can explore alternatives to conventional waste treatment.

There are two kinds of liquid waste:
Black water is waste water from toilets. Because of its bacterial content and the obvious risk of illness, black water must be handled in strict compliance with plumbing codes. If your site is too small (or if your soil "percs" poorly), you may not be able to install a conventional septic system; for alternative equipment, see “Septic and Leach Field Systems” in's Product Guide.
Gray water — the water we’ve used to brush our teeth, wash our clothes, and fill the bathtub — doesn’t pose the same health risks as black water. Where plumbing codes allow, gray water can be used to irrigate gardens, reducing household water consumption. Even if you can't reuse your home's gray water, a heat-recovery device can be installed on a vertical drain pipe to lower your home's energy bills.


Which type is greenest?

Low in cost and easy to work with, polyvinyl chloride (PVC) is a common choice for residential drain, waste, and vent lines. But because of the toxic by-products created in manufacturing PVC, along with the difficulty of recycling it, builders and homeowners may be interested in alternatives. Among them:

  • Cast iron and ductile iron
  • Acrylonitrile butadiene styrene (ABS)
  • Copper
  • High-density polyethylene (HDPE)
  • Vitrified clay (for underground applications)

Due to its high cost, copper already is being displaced for water supply lines by cross-linked polyethylene, so the widespread use of copper for larger diameter drain and vent lines looks unlikely. Before plastic, cast iron was often used for drain lines, and no-hub connections make it relatively easy to assemble.

HDPE has the environmental edge over PVC. Unlike PVC, it is not chlorinated and it has fewer environmentally undesirable additives. It’s also easier to recycle. ABS (a hard, black plastic) isn’t as environmentally attractive. Although it’s not chlorinated, it is difficult to recycle and it also creates some hazardous byproducts as it’s manufactured.

Alternative materials can be harder to find, but growing disenchantment with PVC is likely to change that in the future.

Air admittance valves eliminate a lot of pipe

Suction opens the valve and gravity closes it. Sewer gases trying to escape seal the diaphragm to the rim of the air-inlet basket, which keeps the gases inside the pipe. When a sink is drained or a toilet flushed, this slight positive pressure is relieved because air is sucked in through the basket. This rushing air pushes up the diaphragm, connecting the basket to the drainpipe. After the flush, gravity drops the diaphragm back into place.Plumbing waste systems aren't limited to drain lines. You also need to vent the drain line to keep water in the sink trap. Without this vent, water in the trap can be siphoned out when someone flushes a toilet or drains a bathtub, allowing sewer gases to seep into the house. Vent pipes generally extend through the roof. Cutting a hole in the roof is always riskier than not cutting a hole in the roof, so if you can vent a drain line without going through the roof, all the better. Also, in some situations, like kitchen islands, it's downright difficult to vent the sink.

Air-admittance valves (AAVs) solve these problems elegantly. An AAV allows air to enter the drain system through a one-way valve that then closes by gravity after the sink drains. This valve keeps the water trap sealed and sewer gases out of the house.

About Faucets and Fixtures

In areas of the country where water conservation is important, faucets, showerheads, and toilets should be low-flow models.

All residential faucets for lavatories and kitchen sinks must comply with the maximum flow standard of 2.5 gallons per minute (gpmGallons per minute. Measure of liquid (usually water) flow.) established by the Energy Policy Act of 1992 (EPAct). This standard is about right for kitchen faucets; if the flow is any less, it’s hard to or fill pasta pots quickly or rinse pots effectively. To save water at the kitchen sink, consider installing foot-operated faucet controls.

Flow rates for bathroom lavatory faucets can be significantly less than the Federal maximum without suffering a performance penalty. It’s best to choose lavatory faucets rated at 1.5 gpm or less.

The Federal maximum flow rate for residential showerheads is 2.5 gpm. However, many suppliers offer showerheads that provide a satisfying shower at significantly lower flow rates (in the range of 1.5 to 2.2 gpm).

GBA’s GreenSpec listings include a variety of low-flow showerheads.

Shower Control Gadgets
Several manufacturers sell devices designed to make it easier to:

  • waste less water waiting for a shower to warm (for example, the Evolve Ladybug),
  • turn the shower off when soaping up (for example, the Effishower), or
  • to take shorter showers (for example, the ShowerMinder).

While older toilets used about 4 gallons per flush (gpfGallons per flush. Measurement of water use in toilets. Since 1992, toilets sold in the United States have been restricted to 1.6 gpf or less. The standard for high-efficiency toilets (HETs) is 1.28 gpf.), the Federal government has required new toilets to use no more than 1.6 gpf since 1992. Installing new toilets in a home with pre-1992 models will save a significant volume of water.

Several toilet manufacturers have followed the lead of Caroma, the Australian toilet manufacturer that introduced the first dual-flush toilets to the U.S. These models provide users the option of a standard flush for solid waste and a low-volume flush for liquid waste.

The stingiest flush toilets use 1.28 gpf or less; GBA’s GreenSpec listings are a good place to start.

A more expensive option is a composting toilet. Although composting toilets require almost no water, they are expensive, take up a lot of interior room, and require more maintenance than a flush toilet. Moreover, some building departments will not approve the use of a composting toilet.


If you live in a sunny climate, a solar hot-water system probably makes sense. Those who live in cloudier areas will probably choose a more conventional option like a tank-type water heater, an on-demand heater, or an indirect tank linked to a hot-water boiler. For more information on heating water, go to our discussion of Water Heating.


EPA WaterSense

Image Credits:

  1. Daniel Morrison
  2. EcoInnovation Technologies Inc.
Sep 5, 2010 4:06 PM ET

HDPE Drain Pipes
by Steve R

Where can I get HDPE drain pipes for my new kitchen (sink & dishwasher)? I have been searching for what seems like forever with no luck. I am in need of an HDPE P-trap too, as well as an AAV that will fit. I'm in Pittsburgh.


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