Harvesting Rain: System Design for Strategic Rainwater Capture

Conserving water through rainwater harvesting saves natural resources, providing water for use in buildings and for site irrigation
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Sponsored by Watts Water Technologies, Inc.
Celeste Allen Novak, AIA, LEED AP

Water Conservation

There are many reasons to conserve water resources, such as recent droughts, floods and an aging urban infrastructure. Although water is an abundant resource in many parts of the temperate climate zones of the United States, numerous cities have aging infrastructures that include combined stormwater and sewer lines. With age and the increase of impervious surfaces, the systems of pipes, drains, catch basins and municipal treatment plants, are often overwhelmed when there is a heavy rain. Resultant flooding can cause back-ups into homes and businesses of both sewage and stormwater.

Chart courtesy of BRAE

Rainwater can be substituted for more than 65 percent of household water usage even if just for outdoor use and toilet flushing. If rainwater systems supplied just 15 percent of residential landscape irrigation in the U.S., one billion gallons of water would be saved each day.

The opposite problem occurs in the South and Western United States. Recent weather patterns resulting in historic droughts have reduced aquifers to dangerously low levels. Increased population in cities, the development of new suburbs in areas with a deficit of water resources and the increased demand of agriculture and mining on water resources, add incentives for even more water conservation measures and policies. By August 2000, 36 percent of the United States was in severe to extreme drought, leading to widespread wildfires and other drought-related damages. Instead of too much water, there is too little water to meet the demand for citizens and businesses in the South and Southwest.

Although rules and regulations on the state and municipal level are increasing, most states have an absence of any regulation regarding rainwater harvesting. This void in policy results in disincentives for architects, planners and contractors to incorporate rainwater harvesting in their projects.

One of the most common misconceptions is the definition of rainwater harvesting systems. There are still many regulators and design professionals that still refer to rainwater as gray water and apply gray water treatment standards to rainwater.

Global consumption of water has doubled every 20 years, more than twice the rate of human population growth. According to scientists, shrinking fresh water supplies present the most urgent and potentially catastrophic environmental problem today worldwide.2 The 2006 worldwide average water consumption varies from large amounts of fresh water use by developed countries, to smaller amounts in less developed and less populated countries. The United States water consumption is approximately 570 gallons/per day per person, more than 6 times the amount used in China and substantially higher than most of the world, according to the United Nations Development report.3 In the twentieth century, water seemed to be an unlimited resource. Fresh water drives industrial processes and supports agriculture worldwide. According to the United Nations Environmental Program, buildings consume one-fifth of the world's available water.4 In the twenty-first century, designers are coping with limited water supplies and are learning how to design for smarter water use in buildings.

Rainwater harvesting can conserve water in most residential and commercial projects. Sixty-five percent of household water uses can be substituted for rainwater collected from roof surfaces. These uses include irrigation, toilet flushing, laundry and other nonpotable uses. As a response to dwindling water supplies and a respect for better stewardship of the environment, low impact development (LID) standards are becoming policy initiatives throughout the United States. LID practices encourage rainwater retention, close to the location where it falls to allow infiltration and cleansing. A rainwater harvesting system is designed to absorb and store water to release as needed. Through engineering, land planning, site design and the integration of building systems to resource management, the design professional can save water and enhance watershed hydrology.

Harvested rainwater is ideal for many exterior applications such as washing equipment or windows, irrigating plants and filling swimming pools. Although relatively clean, in all states, rainwater must be separated from the potable water lines to avoid cross contamination. In some states rainwater can be used to flush toilets, wash clothes and provide cooling tower makeup water. Rainwater harvesting reduces the volume of water flowing through aging municipal stormwater systems and decreases the nonpoint pollutant load that enters streams, rivers and lakes. In some states, rainwater can even be used for potable applications.

By storing rainwater, homeowners and businesses will have greater control of their supply of water during peak demand periods or during droughts. They will also see a decrease in their water bills and potentially, their sewage bills. Communities will have less water to pump, treat, redistribute and in many cases can delay upgrades to existing water supply infrastructure. Almost eighty percent of the cost of delivering water is energy according to studies by the Sandia National Laboratory. Conserving water will save energy, water, money and the environment.


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Originally published in June 2013