Benefits of Harvesting Rain Water
The idea of harvesting rain water to be filtered and used as possible drinking water, or as grey water in which rain water can be used for watering plants, flushing toilets and the like, involves the collection, storage and processing of rain water collected from precipitation. If the rain water is being collected from the ground, or below ground it is typically referred to as storm water harvesting. Where rain or storm water is collected from is very important, depending on the environment the water may be susceptible to contamination from pollutants such as mercury, bird feces or bisphenol A (a common unrecyclable organic compound used in plastics).
The collection of rain water is the result of a simple equation:
Rate of litre collection = mm per annum x square meter of collection area
Retail institutions, especially restaurants and grocery stores are high water use buildings due to the nature of the business activities within them. Considering the need for parking at many of these places, the following is a quick analysis on the effects of rain water collection for a retail business building and the savings and ideas for future design considerations which could be implemented.
The average retail building uses 132,610 L of water per year In order to meet that demand in a city exposed to freezing winters, such as Toronto, a tank roughly half the required yearly usage may be required. Such a tank would need to be able to hold 65,000L of water or be 6.2m high with a 3.65m diameter (20’ x 12’ dia), as a worse case scenario.
The average annual precipitation in Toronto is 830mm even though half of that may fall as snow, assume that it is simply being pushed into one of the corners of the parking lot to later melt and be captured in the spring. The current cost for water in Toronto is $39.30/1,000L. Resulting in average yearly expenses of $5,200 per retail building, and consider that most retail developments group together around 10 retail buildings, that’s costs in $52,000 a year of water.
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