Is a Rooftop Cistern Better Than a Ground Cistern?

Advantages of Rooftop Cisterns

Rooftop cisterns, also known as rainwater harvesting tanks, can be a better choice than ground cisterns in certain situations. For instance, in areas with high water tables or where soil conditions make excavation difficult, a rooftop cistern can be a more practical solution. Additionally, rooftop cisterns can be installed on existing buildings, making them a great option for urban or suburban areas.

Design and Installation Considerations

When designing and installing a rooftop cistern, it’s essential to consider the roof material, size, and pitch. A minimum roof area of 1,000 square feet is recommended to collect at least 1 gallon of water per inch of rainfall per square foot. The cistern should be designed to handle the roof’s drainage and prevent backflow into the roof’s gutter system. A first flush device should also be installed to remove debris and contaminants from the roof’s surface.

Cistern Sizing Calculations

To determine the correct cistern size, several factors need to be considered, including rainfall intensity, roof size, and water usage. A general rule of thumb is to size the cistern for at least 50% of the roof’s area. For example, a rooftop with a 2,000 square foot roof would require a cistern with a minimum capacity of 1,000 gallons. However, this number can be adjusted based on the actual rainfall patterns and water usage in the area.