Focus topics

  • indoor water efficiency
  • outdoor water use reduction
  • process water reuse
  • capture/reuse of greywater and/or blackwater
  • rainwater/stormwater use and management
  • Net Zero Water Building (nzwb)

How does the project use water wisely and handle rainfall responsibly? Sustainable design conserves and improves the quality of water as a precious resource. Illustrate how various water streams flow through the building and site, including major water conservation and stormwater management strategies. How does the project relate to the regional watershed? Describe strategies to reduce reliance on municipal water sources. Does the project recapture or reuse water?

Water is essential to all life. We use water every day for cooking, cleaning, agriculture, and manufacturing; even our own bodies are more than 50 percent water! Despite this, many of us take this resource for granted by casually irrigating our lawns, washing our cars, or not repairing leaks or drips. Simultaneously, we are all aware of parts of the country and the world where access to potable water is an ongoing challenge. With climate change, potable water is getting more scare in some regions while others are experiencing a dangerous surplus.

Regardless of where our projects are located, we need to treat water as a valuable resource; it is imperative to use our projects to demonstrate what is possible. In commercial buildings, 95 percent of water demands are for non-drinkable water uses; in residential buildings, roughly 50 percent of water demands are used outdoors. We can do better. As architects, engineers, and members of the building community, we are asked by this measure to show how our projects can treat water with the value that it deserves.

The first step to reducing potable water use is to determine what is really needed. Do we really need to irrigate a lawn, or can we plant self-sufficient natives instead? Do we need to use potable water in our chiller, or can we use captured rainfall or collected condensate? After determining what end uses need to be potable, the next step is to look at low-flow fixtures. Low-flow toilets and sinks are now standard practice; advanced new low-flow showerheads can create the feel of high water pressure using only a fraction of actual water. More ambitious projects can explore systems for purifying rainwater or treating and reusing greywater and blackwater. Many projects can achieve 30 percent reductions over code through smart flush and flow choices; however, we increasingly see solutions that target 50 percent or more. The ultimate success story is a net zero or net positive water building (described below).

Indoor water efficiency

  1. Use low-flow fixtures. Every major fixture manufacturer has low-flow fixtures. From faucets to showerheads to toilets, there are options for every application. (See WaterSense in the resources tab for low-flow fixtures.) To go even further, specify dual-flush toilets, ultra-low-flush urinals, waterless urinals, or composting toilets. However, understand that some of these technologies require additional maintenance and user training.
  2. Calculate the quantity of water used compared to the code baseline. The calculation is based on building occupancy—full-time employees plus visitors or guests—over an annual basis. The Super Spreadsheet has a calculator that will establish a baseline and show a percent reduction of water use.

Outdoor water use reduction

Reduce or eliminate irrigation demand. Work with a landscape architect and/or irrigation consultant to design landscapes that do not require irrigation. If irrigation is needed, best practice is to use collected rainwater and to feed it through a drip system that is weather-smart (inactive during or just after a rain event).

Process water reuse

  1. Depending on the type of building, process water might be used in buildings for industrial or manufacturing purposes (or, in a more typical way, for washing dishes or clothes). Select water-efficient dishwashers, washing machines, and water fountains. (See the link for Energy Star Products below.)
  2. Condensate from HVAC systems should always be captured and used for another purpose, such as irrigation or flushing toilets.
  3. Blower blowdown or chiller makeup water are both necessary to prevent the buildup of sediments in the system; however, these maintenance strategies use excess water in the process. See “Water Efficiency Management Guide: Mechanical Systems” from the U.S. Environmental Protection Agency (EPA) for strategies.

Recapture/reuse of greywater and/or blackwater

  1. Greywater is lightly soiled water that can be reused for non-potable water uses with minimal or no treatment. Common uses of greywater are irrigation and toilet flushing. Best practice is to use all water for multiple purposes before releasing it.
  2. Blackwater is heavily soiled water, from a toilet or commercial kitchen disposal, that is dangerous to humans and cannot be used until treated. Strategies for treating blackwater on-site include engineered composting systems or ecological water treatment systems.
  3. If your building foundation or elevator pits require a sump pump to keep groundwater from causing problems, this water can be captured as an additional source of water. Despite this benefit, foundation pumps are energy-intensive. Best practice is to avoid foundation systems that require pumping whenever possible.

Rainwater/stormwater use and management

  1. Rainwater that falls on the roof is much easier to collect and store than water that falls on the ground. Best practice is to catch this water to use for irrigation. If water collection is not part of the project scope, create a “water collection ready” plan so that a collection system can be installed easily in the future.
  2. The majority of stormwater should be managed where it falls. Projects that manage their stormwater on-site put less pressure on the municipal water system, help to recharge the groundwater supply, and generally keep our water resources cleaner. Strategies for managing water on-site include keeping impervious cover to a minimum and storing water, either for use or for delayed release. The amount of water that runs off the site should match the site’s pre-development conditions.
  3. Because all building sites have some amount of impervious surface, all stormwater cannot be managed on-site without some storage. Options for stormwater storage include above-ground cisterns, below-ground cisterns, or infiltration basins. Stormwater that flows on a site’s surface should be slowed down as much as possible with plants or physical obstacles.

Net Zero Water Building (NZWB)

ILFI defines NZWB as follows: “One hundred percent of the project’s water needs must be supplied by captured precipitation or other natural closed-loop water systems, and/or by recycling used project water, and must be purified as needed without the use of chemicals. All stormwater and water discharge, including grey and black water, must be treated on-site and managed either through reuse, a closed loop system, or infiltration. Excess stormwater can be released onto adjacent sites under certain conditions.”

Additional information

This publication is designed to provide accurate and authoritative information in regard to the subject matter covered.It is published and distributed with the understanding that the publisher is not engaged in rendering professional services.  If professional advice or other expert assistance is required, the services of a competent professional person should be sought.

Image credits

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WRNS Studio

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Nic Lehoux

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Bruce Damonte

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Jeremy Bitterman