Canadian Water and Wastewater Association (CWWA)

Rainwater harvesting: An untapped resource

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Courtesy of Courtesy of Canadian Water and Wastewater Association (CWWA)

The collection of rainwater as a source of relatively clean water has been a common practice of humankind since the dawn of civilization. Before the development of any treatment processes, it was the primary source of potable water for those people without access to other sources of water (rivers, lakes, etc.)

As cities developed, infrastructure became more centralized. Municipalities took over the responsibility of collecting rainwater (stormwater) and generally directing it to the nearest lake or river.

Although household rainwater catchment systems-generally home made, utilizing gutters, downspouts and rain barrels (remember the song?)-were commonly employed to collect water for gardens, those largely faded from the US scene several decades ago. Still rather common in Europe for non-potable applications and widely used in the developing world for all applications, rainwater harvesting is the primary water source available for reclamation and reuse. 

Our air has become increasingly polluted with years of irresponsible behavior by all segments of society and is much dirtier now than when rainwater was coilected and consumed thousands of years ago. As rainwater falls to earth, it picks up particle and gaseous contaminants.

Our drinking water quality standards are constantly becoming more stringent. In spite of this, treating rainwater-and stormwater for that matter-requires generally less technoiogy than any other source of wastewater. The reason for this is because rainwater is the purest of virtualiy all sources of water, is naturally soft and is free of disinfection byproducts.

When used for most non-potable applications (garden watering, landscape irrigation, etc.), it requires little or no treatment. Harvested rainwater costs almost nothing and can significantly reduce dependency on the municipal water provider. As rainwater harvesting becomes more widely used, the decreased stormwater volume will reduce the impact on storm sewers.

Rainwater collection is applicable not only {or houses, but for all other buiidings and structures-virtually anything with a roof. One inch of rainfali provides 620 gallons (2,346.9 L) of water per 1,000 ft, (92.9 m2) of roof area. If a rainwater collection system will be used to produce potable quality water, posttreatment is needed (see Figure 1). A note of caution here: depending on the location, legal restrictions may apply regarding the use of such reclaimed water for potable purposes.

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