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Protecting the Environment '99


Protecting the Environment '99
August 19, 1999

End of pipe: rain supplies their water

2020 Engineering

The Pacific Northwest is well recognized for abundant rainfall that supports a diverse display of plants and animals. The attraction of our natural resources has resulted in continued growth throughout the region. As the human population has grown, so have the impacts from high demands placed on our water resources.

In order to meet our future water needs, new solutions are needed that are both economical and environmentally friendly.

Rainwater harvesting through a collection system demonstrates a simple application of sustainable design. Such a system is independent of any centralized water system and helps to foster an appreciation for water as an essential and precious resource.

Rainwater catchment has been used for water supply since ancient times. Today, it is estimated that there are more than two million rainwater systems supplying household water needs worldwide. More than 250,000 systems exist in the United States.

Examples of areas that actively promote the use of rainwater systems include Australia, New Zealand and Thailand, as well as U.S. states like Hawaii, Texas, Ohio and West Virginia. In Washington, San Juan County recently adopted rainwater catchment guidelines for domestic uses including potable water. However, regulatory changes are still needed to expedite the use of these types of appropriate technologies and methods.

Rainwater catchment system
Owners of this new home in Skagit County will get all the water they need by collecting rainwater from their roof.
Cedar Tree Architects

Rainwater is one of the purest sources of water available. Precipitation in the form of rain, snow, hail or sleet contains very few impurities; it's virtually sodium free as well as being the softest naturally occurring water available. However, once precipitation reaches the earth's surface, there are many chances for minerals, chemicals, bacteria, organic substances and other forms of contamination to enter the water. Water problems have been traced to sewage and wastewater sources that carry synthetic detergents and pathogenic microorganisms. The widespread use of pesticides, fertilizers, insecticides and industrial and medical chemicals, has renewed interest in the quality of water.

In addition to growing concerns about the quality of our drinking water sources, there is now a realization that the amount of water being removed from these sources is also causing problems. Withdrawing excess quantities of groundwater can significantly impact groundwater supplies. In areas where the groundwater tables are lowered due to well pumping, intrusion of salt-water can contaminate the aquifer.

When water is withdrawn from surface water sources such as rivers, reduction of the in-stream water flow can damage fish and wildlife habitat. The recent addition of Chinook salmon to the endangered species list reflects some of the problems associated with the ways we've been managing our water resources.

A roofwater collection system can address both water quality and water quantity issues. Where homes or businesses are designed with "stand-alone" rainwater systems that rely on rainwater only, water no longer must be drawn from sources such as groundwater or rivers. An entire building's needs can be met on-site by rainwater that is collected, stored and treated. Collecting stormwater run-off from a roof also helps address the erosion control and pollution problems related to impervious surfaces.

What is a rainwater catchment system?

The rainwater catchment and graywater reuse systems designed for the Lewis-Loesch home consist of the following components:

  • Controlled catchment surface (metal roof)
  • Gutters (with leaf screens)
  • Downspouts (with filter strainer)
  • Cistern storage (5,600 gallon, food grade, UV resistant polyethylene)
  • Pump (1/2 horsepower to pressurize system)
  • Pressure tank (standard 86-gallon pressure tank)
  • Primary sedimentation filter (20 micron)
  • Secondary sedimentation filter (5 micron)
  • Ultraviolet light disinfection (kills microbiological organisms)
  • Point-of-use drinking water filters (2 stage - 1 and 0.5 micron block carbon)
  • Composting toilet ("Sun-Mar" unit, does not require water)
  • Graywater reuse (subsurface irrigation of a constructed wetland bed)
  • To optimize design of a roofwater collection system, various water conservation options must be reviewed. Water conservation is inherent to any roofwater collection system since the rainwater collected must be able to meet the water demand. A careful water balance analysis, based on historic rainfall data and water use requirements, must be performed to size the storage capacity so that the amount of water collected during the rainy months will provide enough water during drier months. This is also important to assure that the system components (i.e., pressure pump and filters) are properly sized to meet the estimated flow rates.

    Rain can provide clean, safe and reliable water so long as the collection systems are properly built and maintained, and the water is treated appropriately based on its intended use. The amount of filtration and disinfection varies according to whether it is intended for potable uses, including drinking and cooking, or for non-potable uses such as toilet flushing and irrigation.

    Water that is collected and used for irrigation typically requires minimal or no treatment. The minimum treatment could include just a debris screen or use of a sediment filter.

    According to EPA design guidelines for rainwater systems, potable water must be treated to levels that comply with EPA drinking water standards. To meet drinking water standards for individual home systems, simple and non-toxic ultraviolet light disinfection systems can be used that are easy to install and readily available at a very reasonable cost. The use of small standard filtering systems, such as a carbon-block filter, purify the water and remove microscopic particles including giardia and cryptosporidium cysts.

    A real-life example

    A new home in Skagit County has recently been designed to have all of its water needs met by collecting rainwater from the roof. Seattle architect Art Petersen of Cedar Tree Architects designed the house to incorporate a roofwater collection system and to re-use graywater for landscape irrigation.

    "From the beginning, the owners, Cyndi Lewis and Marty Loesch, and myself, wanted to be able to translate our concerns about environmental impact into environmentally friendly behavior, design and construction practices," Petersen said. "Rainwater collection and the re-use of graywater were two of the fundamental design goals."

    Petersen said it didn't cost more to use rainwater collection and re-use compared with a conventional drilled well and septic system.

    "We simply spent the same budget to purchase different components," Petersen said. "Since only the water source and its reuse after leaving the house are different than a conventional house, no special interior systems are required."

    Due to extensive water conservation measures, demand of only 55 gallons per day was calculated for the home (compared to an average of 200 gallons per day for homes connected to public water systems). A waterless composting toilet system cut water demand by half and various types of low-flow water fixtures were used throughout the home to further reduce water consumption.

    Use of graywater for landscaped areas around the home re-uses the collected rainwater in an efficient manner that ultimately returns the collected rainwater back to the local environment. Since the home generates no toilet wastewater, all the water used in the home is classified as graywater which can then be used for subsurface irrigation, according to new Washington State Department of Health guidelines.

    This residential project demonstrates the feasibility of a roofwater collection system in the Pacific Northwest and also provides examples of some other innovative water conservation and water reuse methods that can be applied to other similar or large-scale projects.

    To help more people find practical ways to meet our water needs while protecting our environment, the state Legislature must endorse a progressive policy that supports the exploration and evaluation of alternative technologies. This would include changing current water laws and regulations so that important water issues are handled more efficiently by local communities.

    Prudent planning, development and implementation of new solutions enables a more responsible approach, rather than the more common but less desirable alternative of "crisis mode" decision-making.

    Mark Buehrer, PE, is director and founder of 2020 Engineering, an engineering consulting company in Bellingham dedicated to providing simple, innovative solutions that make communities economically and environmentally sustainable.


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