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How Much Rain Can Your Roof Collect?

Do you want to lend an eco-friendly hand to water conservation efforts by harvesting rainwater? If you’re interested in taking advantage of one of nature’s many gifts, and wondering how much water your roof can collect, then sit tight while we cover the basics of roof water harvesting. 

Collecting rainwater with a roof catchment system is a common and effective method to maximize water supply around the world. Many developing countries with limited access to resources have been using this sustainable water conservation method for ages.

The amount of rainwater that your roof can capture varies and depends on a few factors, such as: the size of the catchment area (roof surface area), local rainfall average totals, type of roof, local regulations, and storage space/capacity. The total square footage of your house (which is the area length multiplied by the area width) is also the size of the roof catchment area. As a rule of thumb, a 1,000 square foot catchment can collect approximately 600 gallons of water per inch of rainfall (at this rate, an annual rainfall of 32 inches would produce 19,200 gallons of free water each year). You can get an estimate of water collection totals for your roof with our rainwater collection calculator to identify adequate storage space and the tank size that you’ll need for storing rainwater. It’s also a good idea to check the local rainfall averages in your area before you start harvesting rain.

The Basics of Harvesting Roof Water

It’s important to determine if your roof surface is safe for capturing rainwater prior to setting up a roof catchment system. Most roofs are ideal for collecting rainwater, but there are some roof types that aren’t suitable for rainwater harvesting, including: old tar and gravel or asbestos shingle, cedar shake, lead flashing sheet, copper, and rooftops treated with biocides. These surfaces adversely affect the quality of water runoff and contaminate it with toxins and other harmful materials.

To start collecting roof water, homeowners need these basic components of a roof catchment system: a collection surface, gutter system to route water, and water storage tanks or barrels. Depending on your usage needs and current setup, various accessories like gutter screens, rain strainers, filters, first flush diverter systems, tank overflow outlets, and storage tank covers – which are available here at Plastic Mart – may be necessary to ensure the quality of collected water. These accessories help to remove any sediment and debris from the rainwater before it enters the storage containers. 

Since rooftops accumulate different contaminants between rainfalls (for example, insect and animal waste, dirt, bacteria, plant or tree matter and debris, etc.), a first flush diverter is essential to filter out the first few gallons of roof water runoff from your main water storage supply. There are many different types of rainwater storage tanks and barrels with a capacity range between 50 and 200 gallons (or more depending on your specific needs). Also, it’s important to note that storage containers will get heavy as they fill up, so they must be placed on a stable and even ground surface. These containers should be periodically inspected and cleaned to prevent water contamination.  

Benefits of Using Roof Water   

The water that your roof collects is ideal for outdoor, non-potable use, such as: landscaping, exterior cleaning activities, or interior applications for toilet flushing and laundry. Additionally, there are several benefits to using collected rainwater, including: lowering the demand on public water sources, maintaining water supply for emergencies and natural disasters, saving money on utilities, and reducing the threat of property flooding.

Plastic Mart offers a large selection of rain harvesting system products and accessories to help homeowners set up their roof water harvesting catchment system. Feel free to contact us with any questions that you may have and start collecting your free water supply today!