Get our free book on rainwater now - To Catch the Rain.
Mattole Community Center rainwater catchment
This project is for greywater usage and may not meet clean drinking water standards. (not potable water)
The Mattole Valley Community Center is looking to install a rainwater catchment system on site in Petrolia, California. The Mattole Board of Directors is interested in having a working rainwater catchment system to water a community garden and also to utilize the project for community outreach and education about the benefits of appropriate technology. This project is starting in January of 2012 and was finished in May 2012.
The objective of this project is to catch rainwater from the roof of the Mattole Valley Community Center in Petrolia. The water storage will help water and accommodate extra irrigation for a flower garden located on site. This project will be a demonstration for the local community and other organizations to learn about the benefits of rainwater catchment, visually show the rainwater catchment process, and along with the utilization of the instructions laid out on this Appropedia site other individuals will potentially be able to produce a system for their own usage.
Ideas for the future
Options to educate also include the creation of an instructional pamphlet or on site graphic image board that explains details on the project or how to make your own system.
Project Evaluation Criteria
The following Criteria will be used to assess the success of this project. These criteria were chosen based on the suggestions of the project coordinator as well as the diligent students who are working on the catchment system. The scale (1-10) represents the importance level of meeting the constraint of each listed criteria.
|Criteria||Constraints|| Weight |
|Community||Will be able to hook up to two inch fire hose from fire truck to supply extra water.|| |
|Maintainability||Must be easy to clean the filter and remove debris, no more than 2 hours maintenance per month|| |
|Aesthetics||Must be pleasing to the eye and look professional|
|Educational Aspect||Must include an educational piece for community (something to explain or highlight the benefit or creation of a rainwater catchment system)|
|Safety & Placement||Must not interfere with walking paths, stairwells, or people's heads!|
|Reproducibility||The structure could be reproduced by local builders|
|Usability||Must sufficiently water the garden on site (with use of hose attachment)|| |
|Cost||Must not exceed budget|| |
|Functionality||Successfully captures and stores rainwater|
Tentative Time Line
|Order Tank||March 8||March 24|
|Build Foundation||March 10||April 8|
|Place Tank on Foundation||March 24||April 15|
|Build First Flush System||March 17||April 15|
|Connect Downspout to Tank||March 25||May 6|
|Test System||March 25||May 6|
Cost of Project - Proposed
|Quantity||Material||Part Number||Source||Cost ($)||Freight ($)||Total ($)|
|1||Norwesco 2500 Gallon Tank||N-40631||http://www.tank-depot.com/productdetails.aspx?part=N-40631||911.99||215.67||1127.66|
|1||Rainwater Collection Adapter for Norwesco Tank||RAINWTNW||http://www.tank-depot.com/productdetails.aspx?part=RAINWTNW||55.99||24.99||80.89|
|Quantity||Material||SKU||Source||Cost ($)||Total ($)|
|2||1-1/2" x 5-1/2" x 18' #2BTR FIR S4S||2618F||Arcata Do-IT Best Lumber||478.00 /MF||17.21 Total Dimensional Lumber : 36.00/BF|
|1||REBAR #5 20.86 97+-/TON +/-||RBAR5||Arcata Do-IT Best Lumber||10.59 /EA||10.59|
|4||Medium L-Angle Z-Max||106518||Arcata Do-IT Best Lumber||2.99 /EA||11.96|
|32||1/2" 2-Hole Strap||517313||Arcata Do-IT Best Lumber||0.12 /EA||3.84|
Options for fill of foundation
|Quantity||Material||SKU||Source||Cost ($)||Total ($)|
|2 Cubic Yard||3/4 base rock with sand||0||Eureka Sand and Gravel Inc.||25.00 / Cubic Yard||50.00|
- 3/4 base rock was chosen for foundation and was picked up from Eureka Sand and Gravel Inc. location in Fortuna, CA in a pick up truck to avoid the delivery cost.
- NOTE: When ordering cubic yards of gravel they can only be purchased in quantities of whole cubic yards.
Another Option for fill of foundation
|Quantity||Material||SKU||Source||Cost ($)||Total ($)|
|2 Cubic Yard||peat rock||0||Eureka Sand and Gravel Inc.||27.00 / Cubic Yard||52.00|
|Delivery||fill for foundation||0||Eureka Sand and Gravel Inc.||300.00 - 500.00||300.00 - 500.00|
First Flush & Filtration
|Quantity||Material||Product||Source||Cost ($)||Total ($)|
|10||3' Gutter Guards||5" K Aluminum Drop-In SCDRPX5ALU||Gutter Supply http://www.guttersupply.com/p-gutter-protection-k-style-drop-in.gstml||2.71 / 3FT||27.10|
|1||3" PVC Pipe||3"x20' Sch40 PVC Pipe Charlotte Pipe Model: PVC 4030B 0600HC||Do it Best SKU: 401617 http://www.doitbest.com/PVC+pipe-Charlotte+Pipe-model-PVC+4030B+0600HC-doitbest-sku-401617.dib?utm_source=shoppingfeeds&utm_medium=googlebase&utm_term=401617&utm_campaign=BROI||29.99||29.99|
|1||3" Abs Sanitary Tee||Genova Inc Abs Model: 81130||Do it Best SKU: 417750 http://www.doitbest.com/PVC+tee-Genova+Inc++Abs-model-81130-doitbest-sku-417750.dib||5.49||5.49|
|1||3" Cap||3" Sc30 Cleanout Fitting Genova Inc Model: 61630||Do it Best SKU: 432035 http://www.doitbest.com/Pvc+Caps+and+Plugs-Genova+Inc-model-61630-doitbest-sku-432035.dib||4.49||4.49|
Estimated Total of Project
The rainwater catchment system will be located on the north side of the Mattole Community Center building. The site for the tank will be located between the existing stairway and the skate halfpipe. The roof and existing gutter system will be used to collect the water. The current gutter system that will be used will only be collecting rain water on the north side of the building's roof and 16' or about 1/3 of the west side of the north roof.
Design for Foundation
The design of the foundation starts by digging a 10' x 10' square pit down past the organic layer to the native soil or the mineral level. This will provide a compact and stable surface to build upon. Four 2" x 6" x 9' pressure treated boards will be used to construct a level and balanced square perimeter that will be fastened together by screws and nails with extra "L" brackets on the ends for improved support. 5/8" rebar will be cut at lengths of 14" and place along each bar; one at each corner 6" from the end and two evenly spaced in the middle 32" from the rebar at the end and each other. About 1.5 cubic yards of 3/4 crushed rock will be poured in and packed to a level surface to a depth of 6" within the constructed perimeter.
Design for Filter
The filter for the system will come from gutter guards that will be placed on the existing gutters to remove organic material that has collected on the roof and other debris. The second filter is incorporated into the intake of the water holding tank and can be removed and cleaned.
Design for First Flush System
The first flush will consist of a "Y septic" connected by an "adjustment connector" from a 1.5" diameter to a 3" diameter ABS pipe that will hold the contents of the first flush. At the bottom of the 3" diameter ABS pipe there will be another "Y septic" connection. This bottom "Y" will have a sealed capped and form the foundation for the first flush system to rest on. The bottom Y septic 3" diameter ABS will have a 2" out line and will have a "screw lid" that will cap the system and can be opened to allow the system to be flushed and cleaned. Between the "Y septic" and the screw cap a small hole will be drilled to allow a slow trickle to empty out the first flush system of its water. Attached to the top Y septic are two 90 degree right angle of 1.5" diameter ABS connected in a "S" shape. These 90 degrees will help prevent debris from entering the tank.
This is a review of the available literature pertinent to rainwater catchment/harvesting systems.
Overview & History of Rainwater Catchment
Rainwater catchment (rainwater harvesting) is an age-old technique of capturing precipitation and water run-off, and storing it for future usage. These man-made systems use gravity to collect rainwater, or run-off, which makes them inexpensive and easy to use.  The water is channeled into a downspout and directed into a holding tank, which can be above or below ground. Various design methods are used to harvest rainwater - from primitive construction to elaborate systems - depending on factors such as budget, usage, climate and geographical location.
“The appropriate design and evaluation of a rainwater harvesting (RWH) system is necessary to improve system performance and the stability of the water supply. The main design parameters (DPs) of an RWH system are rainfall, catchment area, collection efficiency, tank volume and water demand and duration of water demand from the tank. Its operational parameters (OPs) include rainwater use efficiency (RUE), water saving efficiency (WSE) and cycle number (CN). The sensitivity analysis of a rooftop RWH system’s DPs to its OPs reveals that the ratio of tank volume to catchment area (V/A)”</blockquote> 
The captured run-off supplies societies and individuals with a fresh water source and helps enable sustainable living. These catchment methods have been practiced for thousands of years, recoded as far back in time as ancient Rome, where courtyards were paved specifically for catchment, and residencies had individual cisterns to capture rainwater. 
Globally, many civilizations are shaping their cultures and becoming keener on ecological modernization, which favors rainwater catchment and other appropriate technologies. Some regions have mandated collection of rainwater, such as in Gold Coast, Australia, where the City Council declared that all new homes past 2007 must have rainwater catchment set-up for non-potable usage.  Laws such as these assert that rainwater catchment is an important and necessary tool for many areas in the world.
Rainwater catchment is mostly used in areas that are arid or semi-arid, and that may not have a constant flow of run-off annually; areas that are dependent on a local, nearby stream or river; and when the catchment area, volume of storage and capital investment in the system is usually small-scale. 
There are different ways to capture rainwater, and the most common systems are: roof catchment, ground catchment and rock catchment.
This Appropedia page has focused efforts of research on roof catchment systems, which are the most common. There are three main parts to this system, a catchment surface, a gutter and a down spout, and a tank. 
“Rainwater collection systems use gravity to do the work, making these systems easy to use and inexpensive. Rainwater collects into large cisterns, barrels or roof top tanks connected to a down spout that carries it to a holding tank on or under the ground."
Galvanized corrugated iron sheets, corrugated plastic or tiles and thatched roofs with the right type of palm (like coconut)are all good catchment surfaces. Roofs with asbestos or lead based paints should not be used. The roof type and material will affect the amount of water collected. The amount of rainwater available to collect for supply depends on the amount of rainfall and the area of the catchment and the runoff coefficient, which is usually considered to be 0.8 based off of factors such as leakage, evaporation, etc. 
Area Calculation Methods
These are methods used to calculate the amount of runoff/rainwater catchment supply available by area:
Mean Annual Runoff Equation
The most common method is using this equation that demonstrates the amount of supply available: S = R x A x C
Where S = Rainwater Supply, R = Mean annual rainfall, A = roof area in sq meters and C = the runoff coefficient.
The mean monthly rainfall times the roof area is used to calculate the mean monthly roof runoff. Graphing on a monthly basis can display how much water you have during the year to use. A line representing usage can be drawn on the graph to show the extra and the insufficiencies in your system and at what month of the year they will occur. In order to determine potential rainwater supply, reliable rain fall data are required, preferably for a period of at least 10 years. Note, in mountainous regions considerable rainfall variations can occur over short distances.
Statistical and Computerized Methods
- PEquals.com is an efficient way to calculate the estimated runoff amount your roof may supply: www.pequals.com/rain
- Here is another way to calculate water usage.
Once the rain or precipitation lands on the roof, it is diverted into the tank through the following means:
Gutters and Downspout
These lead to the storage tank and incorporate a first flush into the catchment system. A small slope on the roof will help save on costs when it comes to buying materials for gutters. All gutters will divert water into the water holding tank and should have a constant gentle slope to ensure that the water reaches it’s destination and to aide in prevention of blockages.  To collect all available water off the roof all down spouts will need to be directed to the first flush device then to the holding tank.
A general rule is that all gutters should have 1cm^2 of guttering for every m^2 of roof area , or they should have a cross-sectional area of about 200 cm2 to minimize overflow when downpour of rain is very heavy. 
Also know as a foul flush mechanism. This ensures that the waste entering the system that has accumulated on the rooftop between rains is diverted from entering the tank. The amount of water that is diverted from entering the storage tank depends on the size of the roof that is collecting the water. These first flush systems are often simply designed, even a downspout from the root that has a small hand operated diversion valve will suffice. 
An important thing to keep in mind when capturing rainwater is keeping as much waste and debris from entering the system's storage tank as possible. There are different filtration methods available, such as installing screens on each of the gutters or downspouts to keep large particulates out of the system.
Once the water has been captured it is diverted into your holding facility. There are many important factors to consider when storing rainwater. The tank is usually going to be the most expensive part of the system. Here are some things to look for when choosing a tank:
- A solid secure cover to keep out children, animals, breeding insects, dirt, and sunshine.
- A manhole, sump, and drain for cleaning.
- An extraction system that does not contaminate the water; e.g. tap or pump.
- A soakaway to prevent split water from forming puddles near the tank.
- A maximum height of two meters to prevent high water pressure.
- A devise to indicate level of water in tank.
- Lock on the water tap.
- A second sub-surface overflow tank to provide water for livestock, etc...
To determine the size of the tank in your system, you must determine the amount of water that will be utilized and the amount of water that you can catch. (You can use one of the methods of calculating amounts of water collection listed above.)
The location of the tank should be below the level of the roof where the water is being collected and the gutter system to allow gravity to do the work of moving the water to the first flush device and storage tank. In a well designed system, gravity will move water along a continuous downward slope from the roof to the gutter and eventually into the tank. The location of the tank to where the water will eventually be used is also important. It is easier if the tank is located uphill from where the water is needed to provide adequate head pressure to distribute the water by way of gravity feeding. Otherwise a pump will be needed or manually hauling the water up hill or a distance far away will be needed for water distribution. Tank location can be on the surface or sub-surface or a combination of both. A tank that is below the surface will need a pump to retrieve the water back to the surface or a pipe that leads downhill and back out to the surface if this is also where the water is to be used.
When the storage tank reaches its volume maximum or level of water that makes the structure unsafe to hold anymore water, an overflow pipe is needed. The use of an overflow pipe is to purposefully direct excess water out of the tank to a location of choosing other than creating puddles near the tank that could weaken the foundation of the tank, house, or structure. The surplus water could be diverted to another holding tank or to a livestock trough, etc.
The extra water could start to cause erosion if not dealt with and sitting puddles could start to attract breading mosquitoes around the tank.
Cleaning & Sediments:
“As soon as the rain hits the roof it is subject to contamination by pollutants that were deposited on the roof by wind, animals, insects, or by the leaching and dissolving of the material that the roof is made of. If you go outside and look around your house, you’ll get a good idea of what is deposited on your roof between rains. Leaves, dirt, fertilizers, chemicals that you put on your land, animal waste, nearby industrial discharge and just about everything else around you will be blown or dropped onto your roof in some form or another over time.” It is a good idea to clean the sludge and sediment out of your tank at least once a year to prevent build up that can block your system. A valve that can be opened below the outtake tap at the bottom of the tank in order to flush out sediment and sludge will be useful in cleaning.
Taps on roof tanks should be at least 30 cm above the base of the tank as this allows debris entering the tank to settle on the bottom where, provided it remains undisturbed, it will not affect the quality of the water in the tank.
The ground under the tank should be able to hold the weight of the tank when full of water. The area around the tank should have adequate drainage.
During the construction of the gutters, downpipe and tank, it is prudent to have local participation to ensure that the future construction and maintenance of the tanks is accomplished with locally developed skill and that the talent stays in the area . The incorporation of local building materials can allow ease of future building projects. Local material to industrial processed supplies are available for construction. For those made out of organic material, more time on maintenance and replacement will be required. The use of organic building material for the Gutter and Tank for primary use or as reinforcements must be used with caution because of termite, rot, bacterial, and fungal attacks to the system could occur. If using organic material it is encouraged that you treat and or seal it.
Materials for the tank can include: Cement Jars, Concrete Ring Tanks, Ferrocement Tanks, Brick and Block Tanks, Metal Tanks, and preformed Plastic tanks. Tanks should be cleaned annually to avoid build of debris that could affect water quality or block water transportation in the system. Annually cleaning would also help reduce pathogens and other vectors that have built up in the water tank. A tank designed for above ground use has a different design than a tank designed to be put in the ground. Most preformed plastic tanks will have operational standards to their specific design. Most plastic tank walls will start to weaken in constant operating temperatures of 100 degrees Fahrenheit (38 Degrees Celsius). Most plastic tanks can operate around and above freezing but the liquid inside when frozen will expand and could cause a failure of the tank walls if there is no extra room for the expanding substance. Most plastic tanks are not designed to contain pressure or a vacuum and must be constantly vented to atmospheric pressure or the walls of the tanks could fail. Plastic tanks will expand and contract with changes in temperature, so if using tie downs or fastening rings an account of this needs to be made.
Gutter and Downpipes:
The system of gutters and downpipes should also be cleaned annually along with the tank to remove leaves, branches, and other debris that has accumulated over time. The removal of branches that overhang the roof and gutters will alleviate debris buildup and reduce bird and animal fecal matter introduced into the water system.
The types of usage for rain water can be either grey water usages or treated for potable water use.
- Maczulak, Anne. Environmental Engineering: Designing a Sustainable Future. New York, Page 149.
- From the Journal of Environmental Management (Volume 93, Issue 1, Page 147)
- "Rainwater Harvesting Policy Resources", information on Australian law, http://www.oaecwater.org/rainwater-resources.
- Rainwater Harvesting, information on history of harvesting, http://www.tn.gov.in/dtp/rainwater.htm.
- Boers, Th., Rainwater Harvesting in Arid and Semi-arid Zones. Environmental Engineering: Designing a Sustainable Future. New York. Page 1.
- Gould, John. Rainwater Catchment Systems for Household Water Supply. Bangkok, Thailand, page 4.
- Schiller and Latham, (1982)
- Hasse, 1989
- Nagy, Erik. An Analysis of Three Slow-sand Rooftop Rainwater Catchment System Filters. Page 10
- A Simple Rainwater Harvesting Design, http://www.harvesth2o.com/simple_system.shtml
- Roof and Gutters: Safe Materials, http://www.thecenterforrainwaterharvesting.org/2_roof_gutters2.htm