Rainwater harvesting is not new. It has been used around the world for thousands of years. Today, we hear the term more and more, but not in terms of providing potable water for drinking (although many people do) but as a way to provide an irrigation source for landscaping. For instance a roof area of only 1,000 square feet can provide approximately 600 gallons of water during a one inch rainfall.
Containment systems like cisterns and rain barrels are becoming popular again as water quantity becomes scarcer and quality becomes more questionable. Areas known for low rainfall amounts have been using these systems for decades.
The most basic form of rainwater harvesting is simply collecting the water and distributing it immediately to the plants. It’s no surprise this method is referred to as a “simple” system. Rainwater harvesting using a cistern however is classified as a ‘complex’ system but don’t let the name deter you. Complex systems simply refer to storing the water after it is collected and providing a way to distribute the water later.
The term catchment is any area from where the water is harvested. The amount of water harvested from a catchment depends on its size, surface texture, slope and rainfall received. If your roof is 2,000 square feet, and your area averages 20 inches of rain per year, you can harvest 24,000 gallons of water from your roof each year if you have a container large enough to store it.
Runoff is the water that flows off the surface and that could be harvested. This is the water we are able to capture and use immediately or at a later date to irrigate our plants and landscapes
The conveyance system channels the water from the catchment to the storage tank. For example, the holding area is the cistern and the conveyance system would be gutters and downspouts.
Cisterns come in all sizes but I am referring to containers larger than rain barrels. The storage containers can be placed above or below ground and each have its advantages and disadvantages.
Underground cisterns cost more to install, maintain and when it comes to removing the water, a pump is the only option. The biggest advantage to below-ground systems is that these tanks are out of sight, often justifying the higher price. This may be the only choice in some neighborhoods with restrictive covenants.
Above-ground cisterns have the advantage of usually being cheaper to install and maintain, but they are much more obvious and may not be approved in some neighborhoods. Other factors affecting costs in an above-ground system include the type of catchment and conveyance system, the degree of filtration and the distance between the container and the area irrigated. Costs can run around $1,500.
The distribution system is how water is channeled or collected once it has been harvested. In a below-ground system, an electric pump connected to a pipe or a garden hose is necessary to transport the water to a spigot or to the irrigation site.
In a gravity-fed system, flow varies greatly. To optimize the flow rate or pressure, especially if using a drip irrigation or soaker hose system, a pump will be needed.
When it comes to maintaining your cistern, no matter where it’s located, there are certain initial and ongoing steps that should be conducted to keep your system operating properly.
• Make sure to adequately enclose the unit first for safety and to minimize intrusion by animals or breeding of mosquitoes.
• Maintain a debris-free conveyance system. This would include inspecting gutters and downspouts.
• Filters should be cleaned regularly.
• Periodically flush debris from container bottom.
• Inspect your system after a heavy rain and at the end of the rainy season to if any obvious concerns need to be addressed.
• Look for any occurrences of overflow and determine a plan for addressing the harvesting of this excess water if appropriate.
Rainwater is always a good source for plants. It’s free of salts and other minerals that can harm plants and root growth. The harvesting of rainwater can be used in a large-scale environment, such as schools, parks, office parks, etc. But in the home landscape, it’s a relatively easy and inexpensive system to set up and maintain.
After the initial cost of installation (if any), all the water collected and used is free. Not only will you be realizing the savings in real dollars, but more importantly, you’ll be conserving and protecting a valuable resource as well.