Changes

==Design==

==Design==

<h3>Sizing & modeling</h3>

<h3>Sizing & modeling</h3>

{{:Rainwater Harvesting: Sizing and Modelling}}

{{:Rainwater Harvesting: Sizing and Modelling}}

<h3>Catchments</h3>

<h3>Catchments</h3>

Decisions need to be made about the selection and grading of catchments. If one catchment is very large, can it be regraded to drain to two or more outlets? Is it desirable to capture both rooftop water and other stormwater? This will may determine the quality improvements required to  use the water. See table below, which illustrates the higher treatment required for storm water (i.e. non-rooftop).

<p>Decisions need to be made about the selection and grading of catchments. If one catchment is very large, can it be regraded to drain to two or more outlets? Is it desirable to capture both rooftop water and other stormwater? This will may determine the quality improvements required to  use the water. See table below, which illustrates the higher treatment required for storm water (i.e. non-rooftop). </p>

<h3>Cisterns</h3>

<h3>Cisterns</h3>

<p>Preformed above-ground tanks are usually constructed from polyethylene or galvanized steel. They are available with storage capacity up to around 50,000 L. Preformed below-ground tanks may be constructed from reinforced fiberglass or concrete. Fiberglass tanks are available up to around 150,000 L. Concrete vaults can be constructed in almost any size.  Wooden tanks are less common but are also available and permitted in the regulations.</p>     

Preformed above-ground tanks are usually constructed from polyethylene or galvanized steel. They are available with storage capacity up to around 50,000 L. Preformed below-ground tanks may be constructed from reinforced fiberglass or concrete. Fiberglass tanks are available up to around 150,000 L. Concrete vaults can be constructed in almost any size.  Wooden tanks are less common but are also available and permitted in the regulations.

<p>As a standing body of freshwater, RWH cisterns present ideal habitat for [[Pests#Mosquitoes|mosquitoes]]. Mosquitoes should be prevented from entering by using a mesh screen on all openings. Larvicides may be  added when the water is only to be used for irrigation purposes.  

As a standing body of freshwater, RWH cisterns present ideal habitat for [[Pests#Mosquitoes|mosquitoes]]. Mosquitoes should be prevented from entering by using a mesh screen on all openings. Larvicides may be  added when the water is only to be used for irrigation purposes.  

To prevent algal growth, the cistern must be opaque or otherwise protect the water from light.</p>

To prevent algal growth, the cistern must be opaque or otherwise protect the water from light.

<h4>Plumbing and Regulation </h4>

<h3>Plumbing and Regulation </h3>

<p>The current Ontario Building Code requires that rainwater harvesting systems are designed, constructed and installed to conform to good engineering practice. References are made to ASHRAE, ASPE[https://www.aspe.org/content/arcsaaspeansi-63-2013-rainwater-catchment-systems-electronic-download]  and CSA  [http://shop.csa.ca/en/canada/plumbing-products-and-materials/cancsa-b1281-06b1282-06-r2016/invt/27024892006] guides for plumbing detailing. </p>

The current Ontario Building Code requires that rainwater harvesting systems are designed, constructed and installed to conform to good engineering practice. References are made to ASHRAE, ASPE[https://www.aspe.org/content/arcsaaspeansi-63-2013-rainwater-catchment-systems-electronic-download]  and CSA  [http://shop.csa.ca/en/canada/plumbing-products-and-materials/cancsa-b1281-06b1282-06-r2016/invt/27024892006] guides for plumbing detailing.

<p>These guides focus on ensuring that the rainwater does not contaminate or become mistaken for the municipal drinking water supply. Similarly, rainwater must be prevented from becoming contaminated from the sewer. In both cases, an air gap or a back-flow preventer is required.  

These guides focus on ensuring that the rainwater does not contaminate or become mistaken for the municipal drinking water supply. Similarly, rainwater must be prevented from becoming contaminated from the sewer. In both cases, an air gap or a back-flow preventer is required.  

----

----

 

==Performance==

===Performance===

<h3>Water Quantity</h3>

 

In theory a large enough RWH cistern could retain 100% of a single storm. However, sizing a stormwater cistern must account for regulatory requirements, available space, budget, and draw-down i.e. rate of use. If a RWH system is being employed for storm water control, the cistern size will typically be greater than that for optimized potable water use reduction.

<h4>Water Quantity</h4>

In 2007-2010 STEP monitored and modelled three rainwater harvesting systems in the Greater Toronto Area[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. Each system was sized  to balance stormwater management objectives with with potable water use reduction for irrigation and toilet flushing. Key findings include:

<p>In theory a large enough RWH cistern could retain 100% of a single storm. However, sizing a stormwater cistern must account for regulatory requirements, available space, budget, and draw-down i.e. rate of use. If a RWH system is being employed for storm water control, the cistern size will typically be greater than that for optimized potable water use reduction. </p>

*Around 18-20% of the precipitation was lost directly from the rooftop,

<p> In 2007-2010 STEP monitored and modelled three rainwater harvesting systems in the Greater Toronto Area[http://www.sustainabletechnologies.ca/wp/home/urban-runoff-green-infrastructure/low-impact-development/rainwater-harvesting/performance-evaluation-of-rainwater-harvesting-systems-toronto-ontario/]. Each system was sized  to balance stormwater management objectives with with potable water use reduction for irrigation and toilet flushing. Key findings include:</p>

*Annual stormwater capture varied between 18 and 42 %.

<h3>Water Quality</h3>

<li>Around 18-20% of the precipitation was lost directly from the rooftop.</li>

<li>Annual stormwater capture varied between 18 and 42 %.</li>

 

<h4>Water Quality</h4>

{{:Rainwater_harvesting:_Water_quality}}

{{:Rainwater_harvesting:_Water_quality}}

----

----