This Microsoft Excel-based tool was developed to assist with the design, sizing and costing of residential and commercial scale rainwater harvesting systems.  The tool is relatively simple and easy to use and has been verified against actual monitoring data.  Simply provide information about your rainwater harvesting project – such as roof area, number of building occupants, and proposed rainwater uses -   and the tool will calculate the optimum size of the rainwater storage tank and system components, and provide an estimate of how much the rainwater harvesting system will cost. 

How much water you save will depend on how you size your tank.  Various criteria are provided for tank sizing.  For instance, the tank can be sized to:

• Maximize potable water savings while keeping tank size to a minimum
• Meet a specific water conservation target (i.e., reduce municipal water use by 30%)
• Provide rainwater supply for a specified time period without rain (e.g. 14 days)  and
• Meet stormwater management requirements (i.e., collect all rainfall from a 5-year storm 24 hour event)

Give the tool try and let us know what you think at step@trca.on.ca