WATER EFFICIENCY
Every Precious Drop
By 2020 our homes and communities will consume much less water than today, using the latest technologies to record individual water use and minimize waste. By combining high-efficiency fixtures and appliances, structured plumbing design, weather-based irrigation controls, and graywater reuse systems, residential consumption will drop from 60 gallons per person per day down to 20.
Alejandra lives in a hyper-water-efficient home. As she steps out of the shower, the water leaving the drain trickles into a gray-water holding tank where it mixes with water from the kitchen and bathroom sinks and the clothes washer. After drying herself, she places her towel in a spin dryer that extracts the moisture and delivers it to the graywater tank. When she flushes the toilet, filtered and treated water from the graywater holding tank refills the 0.5-gpf toilet. Later, a subsurface irrigation system delivers a precise amount of treated graywater to plants in her landscape, controlled by soil moisture sensors in the ground and microsensors on the leaves of the plants. An ultra-thin flat screen near the kitchen sink shows her water use for the day and month to date, the amount of graywater in her holding tank, as well as her current energy consumption and solar generation from the panels integrated into her roof tiles. She uses about 20 gallons of potable water per day, and her family of four uses less than 2,500 gallons of water per month for both indoor and outdoor purposes. Welcome to the future.
The good news is, we’re not that far away, at least technologically, from creating Alejandra’s hyper-water-efficient home. The bad news: Some political, economic, and legal barriers must be addressed for us to get there.
We have made progress in reducing our household water use. Research shows that with today’s best-available water-efficient technology people are already using less water; they use on average 35 gallons per capita per day (gpcd) indoors as opposed to the 69.3 gpcd recorded in the standard homes of the past. But to achieve the low water-use levels of Alejandra’s water-efficient home, we need to reduce both indoor and outdoor water use to a level of 20 gpcd, which will require significant changes in the way we plumb and landscape our houses.
TOWARD 2020: HOME OF THE FUTURE
The hyper-water-efficient home of the future will have hot showers, clean clothes, and beautifully landscaped yards, but how it will deliver these differs from today’s water-efficient homes in three significant ways:
Graywater. Bath, shower, sink, and clothes washer wastewater will be collected, filtered, treated, and stored in a holding tank until needed for flushing toilets and irrigating plants. Although graywater systems can be installed today (if local rules permit), in the water-efficient home of the future they will be more common, more affordable, and easier to use and maintain.
No water will be used for outdoor irrigation beyond what is supplied from the graywater system. Plants will be selected based on their ability to thrive in local climate conditions. Graywater will be transported to the landscape through a subsurface system that directs water to plants based on the measured soil moisture content and on tiny sensors on the plants. Every grouping of plants will have its own irrigation zone. The entire system will be controlled through the home computer using a custom graywater irrigation app. The system will continually monitor for faults and leaks, and any problems detected will be catalogued and electronically delivered via an alert system.
Rainwater. Rain that falls on the hyper-water-efficient house will be used to irrigate through the landscape design itself. Downspouts from the roof will direct rainwater onto the landscape to be dispersed across plant beds and detained with berms and furrows allowing the water to gradually infiltrate the ground. Rainwater capture, storage, and reuse will be part of future water-efficient homes in regions where the timing and frequency of rain events make such a system cost effective. In many areas, integrating rainwater runoff in the landscape design is the most cost-effective approach.
Resource Consumption Dashboards. Families that live in hyper-water-efficient homes will need regular feedback on water use provided by a flat-screen monitor on the kitchen wall dedicated to water and energy consumption. Daily, monthly, and annual water use will be compared with the pre-established consumption goal or budget (see illustration on page 35).
The water level in the graywater storage tank will also be monitored, along with measured soil moisture levels at any sensor point in the landscape. The dashboard will also be used for scheduling irrigation, leak alerts, and identifying when lights and appliances have been left running.
Among some of the other features in these ultra-efficient homes: 0.5-gpf toilets, 10-gallons-per-load clothes washers, 4-gallons-per-load dishwashers, structured plumbing that reduces hot water delivery waste to less than 1 cup of water, and indoor moisture capture to extract moisture from wet towels.
GETTING THERE
Achieving greater water efficiency will require improved technology, reduced hardware costs, consumer behavioral changes, legal and policy changes in health codes, and re-interpretation of some water laws. Graywater systems must get less expensive and easier to maintain. Installation costs can exceed $10,000 for a whole-house system, not counting ongoing maintenance and electricity. If 30,000 gallons of water per year is saved for a household of four, the economic benefit is just $300 per year—a 30-year payback for the capital costs associated with the system. Even an installation cost of $3,000 will have a payback exceeding 10 years once maintenance is considered. Until whole-house graywater systems can be installed for under $1,000 per house, the economics are not likely to favor widespread adoption, even if the cost of water dramatically increases.
There are other significant barriers to the widespread implementation of graywater recycling. Health codes will need to be modified to incorporate standards for the filtration and treatment of graywater to enable health departments to assess risks associated with the use of this water and to permit installation of these systems.
Some important progress has been made. The International Association of Plumbing and Mechanical Officials has approved a graywater code section in Chapter 5 of the Green Plumbing and Mechanical Code Supplement, now Chapter 16 of the Uniform Plumbing Code. The water rights issues associated with graywater may be more challenging, depending upon the jurisdiction. A strict interpretation of a “single-use water right” may prohibit the use of graywater recycling. Some cities in the western United States have only single-use water rights. In regions where water can be used to extinction, water rights should not pose a barrier to graywater recycling.
Landscape guidelines need to be in place to address regional irrigation requirements and to define improved irrigation technologies. In wet regions, high-water-use plants and large turf areas can remain. In dry regions, only plants that can manage with minimal irrigation will be included. Tools like advanced irrigation control technology, including soil moisture sensors, rain sensors, and evapotranspiration weather stations, have become more affordable over the past 10 years. This is good news for consumers, but the key to achieving 20 gpcd is to eliminate wasteful irrigation entirely.
The landscape itself should be designed to rely on available precipitation supplemented only with small volumes of reuse water. And the key to this is using smart technology, from microsensors to multi-zone drip systems. High-pressure irrigation systems like those we use today will only be an option for parks and large landscapes. Low-pressure, micro-managed drip irrigation that uses recycled graywater will be the state of the art.
And the technology to produce the resource-use dashboard described in Alejandra’s kitchen exists today and is in use in green commercial buildings with sophisticated metering, but residential dashboards are still rare because of the lack of household meters that can provide real-time feedback. Even though dashboards can be created with the monthly water meter readings of today, their true informational value will not be realized without a smart meter that delivers information on up-to-the-minute water use. Advanced metering infrastructure is expensive, and while these meters are increasingly being installed by water utilities, few have harnessed the potential power of these systems to provide customers real-time information on consumption.
THE FUTURE IS WAITING
Indoor water use is dropping with new high-efficiency plumbing fixtures and appliances. Outdoor water use can be reduced with technological improvements in sensors and irrigation equipment. These advancements will bring us closer to the hyper-water-efficient home of 20 gpcd. What we further need are approvable and affordable graywater systems, widespread smart metering, and readily available sensor technology. All of this is possible by 2020. Where the impediments are most serious are where water rights laws will prevent water capture and reuse at the individual household level.
Overcoming these challenges will be well worth the effort: If we can achieve nationwide a residential usage level of 20 gpcd or less, that would mean that a city such as Phoenix could reduce its overall water demand by 70% or more. Our sustainable water future needs this!
Mary Ann Dickinson is executive director of the Alliance for Water Efficiency (AWE) and Vision 2020 Water Efficiency co-chair with Carole Baker, chair of AWE. Peter Mayer is vice president of Aquacraft, Inc., a firm that specializes in residential end-use measurement.
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