Rainwater Capture and Storage
A modern approach to the old rain barrel.
The emergence of prolonged periods without rain combined with increasing intensity of rain events is making the capture and storage of rainwater a priority. The Common Ground Community Garden, with the help of Christopher Harrison of Harrison Regen, recently installed a new gutter and 275-gallon roof runoff collection tank on the 6’x10’ shed roof on our site for this purpose. This runoff collection and storage system will: reduce runoff hitting the ground during precipitation events of higher intensity and thus reduce erosion, as well as reduce reliance on the public water system (and the chlorinated water it supplies) for irrigation, simply by tapping into (pun intended) the rain that falls freely from the sky.
Other reasons for rainwater capture include: reducing withdrawal from underground aquifers, with their attendant energy requirements and their salting of the soil where used for irrigation, passive replenishment of swimming pools, and even the provision of water for non-potable and even potable household uses. The system installed at the GLGWL Common Ground Garden, however, is only suitable for non-potable garden uses, for reasons that will be described below.
Here is a diagram of the system installed at GLGWL Common Ground Community Garden:
* The gutter should be sloped very slightly towards the gutter downspout to ensure that water flows towards the downspout.
** The tank orifice should be covered with a piece of aluminum screen held in place with a 6” hose clamp to keep out debris for a free-flowing system as opposed to a hard connection system. In the free-flowing system such as this the orifice serves three functions: the inlet, overflow, and vent. For a hard connection system, a dedicated overflow needs to be installed in the side of the tank and a vent in the top, as well as a first-flush diverter to the 4” PVC pipe carrying water from the downspout to the tank inlet.
One of the challenges of using a clear IBC tote such as we did for this project is that it allows sunlight to shine into nutrient-laden precipitation, which causes algae to grow. Therefore, the tank must be made opaque enough to prevent any sunlight from coming in to disadvantage the algae’s growth. In this case, we wrapped the tank in two 6’x8’ tarps held to the tank frame with bailing wire and held down on the top with bricks to keep out the sunlight. Bricks were also used to prop up the back end of the discharge pipe and hold it in place to ensure the pipe slopes down from the downspout to the tank inlet.
The beauty of this system is that it can be easily installed by 1-2 people with just moderate construction skill. However, this has the tradeoff of requiring slightly more observation and maintenance than closed-piped systems. Regular maintenance activities include:
Check system during each visit, but especially during/after rain events, ensure that discharge is flowing into tank inlet, and clear inlet screen of any dirt and debris.
Before the winter freeze, reduce the tank volume to 75% full, close 2” tank outlet valve, and open or remove the hose bibb assembly.
Inspect the gutter every fall during and after the leaf drop, and keep it clear of leaves and debris.
Every 1-2 years (ideally when the tank is low or empty), drain out completely, remove the 6” hose clamp and screen, remove the hose bibb assembly while leaving the 2” tank discharge open, and then clean the inside with a jet spray from a pressurized hose. When the water flowing out the drain no longer shows any dirt or debris, the tank is clean and ready to be put back into use.
One of the keys to understanding the volume of rainwater available for capture is through some simple mathematical calculations. If we know the size of the roof, we can easily estimate how many gallons of runoff that roof can produce per inch of rainfall.
Width (ft) x Length (ft) / 12 (in/ft) x 7.48 (gal per cubic ft) = Gallons of water per Inch of Rain
The GLGWL shed measures about 6’ x 10’. So plugging into the formula above yields: 6’ x 10’ / 12 (in/ft) x 7.48 gallons per cubic ft = 37.4 gallons per inch of rainfall
Considering that Greenwood Lake, NY receives an average of 43” of rain equivalent (including snow) each year, this means that the 6’x10’ shed roof can provide up to 1,600 gallons of runoff to be harvested and stored. Note that this calculation helps to demonstrate why individual 55-gallon rain barrels, while helping to raise awareness about runoff capture and storage, are quite inadequate to the task of effective water capture and storage.
The Bill of Materials for this project are included below in case you want to try building a similar system for your own use. For further – and much more detailed – reading, we recommend checking out Water Storage: Tanks, Cisterns, Aquifers and Ponds by Art Ludwig (Oasis Design, 2005-2013). It is undoubtedly the most comprehensive book available on this subject, and is the result of decades of practical application and research by the author. Base principles and links to purchase all of the author’s work can be found at his website, www.oasisdesign.net.
Bill of Materials:
Gutter, end caps, drop outlet, coupling seamer, short downspout pipe, leaf screen
1/8” pop rivets for attaching gutter and downspout pieces together.
4” PVC pipe, 90-deg. elbow, and 22.5-deg. elbow for piping from gutter to tank
Used (non-toxic) 275-gal International Bulk Container (IBC) tote, washed out
2” PVC female adapter, 2” smooth PVC plug, 1/2” x 1/2" threaded female adapter union fitting, and 1/2” brass hose bibb for outflow (garden hose connectable)
Aluminum screen held over opening in top of tank by 6” hose clamp for debris screen
(2) bags of 3/4" gravel and (4) concrete blocks for tank foundation
Old bricks, to keep 4” PVC pipe in place and sloped towards tank opening as well as holding down tarp folded over top of tank.
(2) 6’ x 8’ light duty tarps for UV screening and galvanized bailing wire to anchor tarps to IBC tote frame
Silicone sealant for sealing joints inside of gutter, PVC primer and cement for outflow adapter
If you need any help or guidance with a similar project you can also reach out to Christopher Harrison of Harrison Regen by phone or text to 845-545-5860, or by email to owner@harrisonregen.com.