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A study of many types of roof surfaces in Texas found:

A study of many types of roof surfaces in Texas found:

*'Cool' membrane, concrete tile, and metal roofs all produced water of similar good quality for non-potable use,

*'Cool' membrane, concrete tile, and metal roofs all produced water of similar good quality for non-potable use,

*The runoff water from asphalt shingle and green roofs contained significantly more dissolved organic carbon (DOC). The DOC can add a  yellow colour to the water. If the water is treated with chlorine, for drinking purposes, DOC can produce toxic compounds [http://www.sciencedirect.com/science/article/pii/S0043135410008535].

*The runoff water from asphalt shingle and green roofs contained significantly more dissolved organic carbon (DOC). The DOC can add a  yellow colour to the water. If the water is treated with chlorine, for drinking purposes, DOC can produce toxic compounds<ref>Mendez CB, Klenzendorf JB, Afshar BR, et al. The effect of roofing material on the quality of harvested rainwater. Water Res. 2011;45(5):2049-2059. doi:10.1016/j.watres.2010.12.015.</ref>.

Research in Hamilton, ON assessed the water quality of rain collected from three highly reflective 'cool roof' membranes[http://wst.iwaponline.com/content/70/7/1205?utm_source=TrendMD&utm_medium=cpc&utm_campaign=Water_Science_and_Technology_TrendMD_0]. Key findings:

Research in Hamilton, ON assessed the water quality of rain collected from three highly reflective 'cool roof' membranes<ref>Gong K, Wu Q, Peng S, Zhao X, Wang X. Research on the characteristics of the water quality of rainwater runoff from green roofs. Water Sci Technol. 2014;70(7).</ref>. Key findings:

*The water was free from significant contamination with by-products of plastic manufacture and did not show elevated levels of the five metals tested.  

*The water was free from significant contamination with by-products of plastic manufacture and did not show elevated levels of the five metals tested.  

*Increased microbiological contamination was found in runoff from roof areas where ponding occurred.

*Increased microbiological contamination was found in runoff from roof areas where ponding occurred.

Note: Increased microbiological contamination in roof runoff is also associated with warmer weather [http://www.sciencedirect.com/science/article/pii/S0043135411002181].

Note: Increased microbiological contamination in roof runoff is also associated with warmer weather <ref>Vialle C, Sablayrolles C, Lovera M, Jacob S, Huau MC, Montrejaud-Vignoles M. Monitoring of water quality from roof runoff: Interpretation using multivariate analysis. Water Res. 2011;45(12):3765-3775. doi:10.1016/j.watres.2011.04.029.</ref>.

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