Achieving Net-Zero Residential Landscapes

Net-zero water use is a tangible strategy for creating integrated systems that minimize the impact of our landscape designs on precious water resources. At the 2011 ASLA Annual Meeting, Bobby Markowitz, ASLA, Earthcraft Landscape Design, Marilyn Crenshaw, AIA, The Green Architect, and Bill Wilson, Environmental Consultant at Carlile Macy, presented straightforward strategies for understanding and achieving net zero.

There are typically three sources of water available on a property: potable (municipal) water, rainwater, and graywater. Potable water is energy intensive to collect, treat, and deliver, and the environmental repercussions of its extraction can be devastating. Rainwater is delivered directly to the site free of charge and can often be employed for potable uses (with some form of sterilization, depending on codes). Graywater is water used in household fixtures such as sinks and laundry machines (excluding unsanitary blackwater) and can be reused for irrigation in the landscape. If primary sewage treatment occurs onsite, treated blackwater is also a potential source for irrigation.

Net-zero water use in this context refers to the efficient use of rainwater and graywater onsite, such that the demand for potable water is reduced or eliminated altogether. According to Bobby Markowitz, ASLA, Earthcraft Landscape Design, the heart of net-zero is a simple equation: make demand equal supply. “That’s how you get to net-zero.” In order to do this, the designer must quantify all sources of water and all water losses occurring on the property and then design an integrated water management system that captures water and uses (and reuses) it in the household and landscape.

“The first thing I look at is calculating roof runoff,” said Markowitz, “then I consider storage capabilities.” The amount of rainwater that can be harvested from a building can easily be calculated by multiplying the area of the roof by the average amount of rain for the region (adjusting for units of course). The same is true for any impermeable surface that water can be collected from. Following that,  above and below ground storage opportunities such as tanks and cisterns can be investigated.

A little more research is required for the other parts of the equation. There are a couple of strategies that can be used to grasp the water demand of a household. One is to use flow meters, which can measure the amount of water flowing out to irrigation. The other is to look at the water bills. “Interior use is basically the same all year,” said Markowitz. The spike in the summer is irrigation (note: this session was California-based, and water use will vary by climate). The potential amount of graywater produced can be understood by looking at the number and types of fixtures and their average use. 

Once potential onsite water capture and household use are estimated, an equation is created, and the task becomes to “tweak demand to make it equal to the supply.” If rainwater can be used in the interior, then household water use can be subtracted from rainwater on the supply side. The rainwater left over plus graywater is then available for landscape requirements, which can be adjusted through the plant palette as well as by improving irrigation efficiency. Markowitz recommended a number of methods for improving irrigation efficiency, including the use of subsurface capillary irrigation and smart controllers that sense soil moisture or estimated evapotranspiration rates. Designing the integrated water management system, which includes the various water sources and uses, requires careful orchestration of numerous components, including storage, pumps, filters, and some specialized plumbing.

While recent progress has been made to codify these types of water use, achieving net zero in residential landscapes often necessitates working closely with public officials so that progressive strategies will be embraced. Marilyn Crenshaw, AIA, The Green Architect, recounted a project that involved the integration of rainwater, graywater, blackwater, and green roof systems. She said her success depended on the approval of numerous agencies, including planning, public health, public works, and the fire marshall. Crenshaw recommended making personal contact with local officials, listening to their concerns, and learning how to speak their language. Crenshaw also suggested that net-zero designers can make the most of restrictive codes and even get credit for voluntary rating systems. For instance, the Sustainable Sites Initiative (SITES) has a requirement to reduce potable water use for landscape irrigation by fifty percent from established baselines. Net-zero strategies can reduce potable water use by 100 percent.

The environmental benefits of net-zero water use are significant. Bill Wilson, Environmental Consultant at Carlile Macy, is motivated by his observations while conducting oceanic research. He has found that massive amounts of small plastic debris are entering the ocean and being consumed as plankton. The source of this plastic is primarily urban wastewater and runoff. Wilson noted that wastewater can be treated by bacteria in soil, but the ocean is not very well equipped to process and decompose urban waste. “My goal is to get this wastewater out of the ocean and onto the land where it belongs,” he said.

Landscape architects and architects can use water-related environmental problems such as reservoir depletion to inspire clients who may be interested in net zero water use to take action. However, Markowitz noted that return on investment calculations, which are often used to sell sustainable technologies such as alternative energy, do not work very well with water. This is because “water is such an undervalued resource.” The price of water does not sufficiently reflect its growing scarcity or the embedded costs of public infrastructure. However, as Markowitz said, “if you want to know the value of water, try not having any.” Wilson said that clients will be motivated by knowing that they will have a secure water supply in an emergency situation while their neighbors are helpless – which he calls “the smugness factor.”

While it may not always be possible to achieve net-zero water use at a site, it is certainly a worthy goal to make the most of our precious water resources. Furthermore, looking closely at the numbers and thinking of the landscape as a component of an overall water equation provides a pragmatic and powerful tool for quantifying the landscape’s role in sustainability. It is also an opportunity to expand the role of the designer, as net-zero residential water use requires the integration of landscape architecture, architecture, and the various trades. Increasing water scarcity, like global climate change, needs to become a rallying point for the various disciplines to come together and look at projects as holistic systems that are connected to the broader ecological systems we all rely on.

This guest post is by Dakotah Bertsch, Associate ASLA, Design Associate, Design Ecology

Image credit: Rain on vegetation / Flickr

3 thoughts on “Achieving Net-Zero Residential Landscapes

  1. bobby 11/10/2011 / 3:40 pm

    Dakotah – great job – you got it and i am glad to give it!! best wishes, Bobby Markowitz

  2. Jordan Iversen 11/10/2011 / 4:52 pm

    Great article! Rainwater harvesting is definitely the future. Keep up the good work Bobby!

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