Rainwater harvested from the roofs provides a high-quality source of water to be used throughout your property for washing, toilet flushing and even safely consumed with proper precautions. When purchasing water tanks for storing rainwater, knowing how much water you can harvest may influence the quantity and size of water tanks you purchase.
This article is one in a two-part series to help you know how much rainwater you can harvest. In a previous article, we looked at how to find out the rainfall in your area. This article will help you to understand your capture area and how much rainwater it can yield.
Calculating the Surface Area of Your Roof
Rainwater is harvested from rooftops. Stormwater is rain that hits and runs over ground surfaces whether pathways, driveways, decks and the like. As such, you will need to calculate the surface area of rooftops that will be used as rainwater capture areas. This includes your rooftop as well as its gutters.
To do this, you can either get a tape measure for absolute precision. Or, if you don’t have one handy you can estimate by stepping along the outside of your house, shed or other building structure.
The average step of a person walking casually is around 0.76 metres long. So, if it takes you 15 steps to walk the side of your house, that is 11.4 metres (0.76m x 15). Assuming your house is rectangular, once you know the length and width, you simply multiply both together. So 15 steps (11.4m) by 22 steps (16.72m) provides a rainfall capture area of 190.6m2 (11.4m x 16.72m).
It is important to note that 1mm of rain falling on 1m2 of wet roof area will yield 1 litre of water. So then, if 100mm of rain falls in a summer week (as happens throughout coastal areas of Australia), then a roof size of 190.6m2 will yield 19,060 litres of rainwater (100mm x 190.6m2).
Warning of Roof Capture Areas
Take care to not harvest water from rooftops with lead flashing or treated timber. Flashings are strips of metal used to stop water penetrating the junction of a roof with another surface. Some older homes may contain lead flashings and it is important to either replace or avoid them entirely. Lead is toxic and while many homes in Australia no longer have them, always take a safety-first approach to make sure.
Clark Tanks is committed to providing quality tanks and products designed to meet the needs of Australian home owners, farmers and industries. When you invest in a product to do an important job, you want to know your investment is a good one. Our friendly staff are happy to advise and provide a competitive solution that meets your needs.