Literature Review

This page describes some of the basics behind designing Rainwater Catchment Systems. It is a collection of resources pulled from similar projects that are documented throughout Appropedia, and contains helpful resources for those interested in learning more. Please feel free to add even more helpful content!

Rainwater Catchment

A rainwater catchment system is a system that collects, filters, and stores rainwater for community or household use. [1]

Rainwater catchment offers significant advantages over other sources of water (e.g. surface water and groundwater). Water that has reached the ground has had an opportunity to entrain or dissolve constituents from soils, rocks, or other surfaces, which can contribute qualities that are undesirable. The most undesirable qualities would include pathogens, carcinogens, or other contaminants. Rainwater, by contrast, is subjected only to contaminants that it reaches as it descends through the atmosphere and as it flows on the collection surface. As opposed to other water treatment methods, hydrologic, solar-driven evaporation requires no funding, but rainwater supply is susceptible to seasonal and climactic variations in quantity and frequency. [2]

Rainfall

One of the first steps to designing a Rainwater Catchment system is to determine the amount of rainfall that will fall in the desired location. A good practice is to determine the average precipitation depth in inches for each month. This data can typically be found from sources such as the PF Data Server from NOAHH.

Catchment Potential

Besides the amount of rainfall that is available to be collected, the size of the collection surface will determine how much of the available rainfall will be collected for usage. Sites such as the Rainwater Collection Calculator and Basic Rainwater Collection Calculations can aide the design process.

Roofing

The type of construction material is important for a rainwater catchment system. Depending on what material is used for the roof, the collected water can be contaminated by carcinogens[1]. The roofing materials used in a rainwater catchment system should be chemically inert to keep contaminants out of the system. In addition to the roof material itself, the climate can influence the contaminate runoff depending on the material.

Types of Roofing Material

The following are brief descriptions of a few common roofing materials and their benefits and drawbacks when being considered for Rainwater Catchment Projects.

Thatch: Filler

Wood: Filler

Tile: Filler

Concrete: Filler

Metal: Filler

Water Quality

There are three criteria to having acceptable quality drinking water.

  • No fecal bacteria
  • No harmful chemicals
  • No bad taste or smell

Rainwater catchment systems have commonly found contaminants due to the location and isolation of rooftops.

Common contaminants of rainwater catchment systems[3] [4]
Contaminant Source Risk of entering Rain Tank
Dust and Ash Surrounding dirt and vegetation
Volcanic activity
Moderate:Can be minimized by regular roof and gutter maintenance and use of a first-flush device
Pathogenic Bacteria Bird and other animal droppings on roof, attached to dust Moderate:Bacteria may be attached to dust or in animal droppings falling on the roof. Can be minimized by use of a first-flush device and good roof and tank maintenance.
Heavy metals Dust, particularly in urban and industrialized areas, roof materials Low:Unless downwind of industrial activity such as a metal smelter and/or rainfall is very acidic (this may occur in volcanic islands)
Other inorganic
Contaminants(e.g. salt from seaspray)
Seaspray, certain industrial discharges to air, use of unsuitable tank and/or roof materials Low:Unless very close to the ocean or downwind of large-scale industrial activity
Mosquito Larvae Mosquitos laying eggs in guttering and/or tank Moderate:If tank inlet is screened and there are no gaps, risks can be minimized.

Filtration

Filtration is necessary not only for the quality of the water but also for the longevity of the rainwater catchment system. The first instance of necessary filtration occurs right after the rainfall makes contact with the piping that leads it away to the storage. Detritus such as leaves, twigs, and other large objects need to be removed in order to prevent clogging within the system. Common methods for the removal of such objects are grit screens that can be manually cleaned with ease. Depending on the desired uses of the water, additional filtration may be necessary.

When considering water usage for human consumption, the following types of filtration must be considered in order to remove smaller particles and pathogens. [5]

Carbon/Activated Carbon: "Activated carbon chemically bonds with and removes some contaminants in water filtered through it. Carbon filters vary greatly in effectiveness: Some just remove chlorine and improve taste and odor, while others remove a wide range of contaminants including asbestos, lead, mercury and volatile organic compounds (VOCs). However, activated carbon cannot effectively remove common “inorganic” pollutants such as arsenic, fluoride, hexavalent chromium, nitrate and perchlorate. Generally, carbon filters come in two forms, carbon block and granulated activated carbon."[6]


Carbon Block: "Carbon block filters contain pulverized activated carbon that is shaped into blocks under high pressure. They are typically more effective than granulated activated carbon filters because they have more surface area. Their effectiveness depends in part on how quickly water flows through."[6]


Granulated Activated Carbon: "These filters contain fine grains of activated carbon. They are typically less effective than carbon block filters because they have a smaller surface area of activated carbon. Their effectiveness also depends on how quickly water flows through."[6]


Ceramic: "Ceramic filters have very small holes throughout the material that block solid contaminants such as cysts and sediments. They do not remove chemical contaminants."[6]


Deionization: "These filters use an ion exchange process that removes mineral salts and other electrically charged molecules (ions) from water. The process cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms. EWG’s water filter guide does not include any filters based on this technology."[6]


Distillation: "This technology heats water enough to vaporize it and then condenses the steam back into water. The process removes minerals, many bacteria and viruses and chemicals that have a higher boiling point than water. It cannot remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). EWG’s water filter guide does not include any filters based on this technology."[6]


Ion Exchange: "This technology passes water over a resin that replaces undesirable ions with others that are more desirable. One common application is water softening, which replaces calcium and magnesium with sodium. The resin must be periodically “recharged” with replacement ions."[6]


Mechanical Filters: "Like ceramic filters, these filters are riddled with small holes that remove contaminants such as cysts and sediments. They are often used in conjunction with other kinds of technologies, but sometimes are used alone. They cannot remove chemical contaminants."[6]


Ozone: "Ozone kills bacteria and other microorganisms and is often used in conjunction with other filtering technologies. It is not effective in removing chemical contaminants. EWG’s water filter guide does not include any filters based on this technology."[6]


Reverse Osmosis: "This process pushes water through a semi-permeable membrane that blocks particles larger than water molecules. Reverse osmosis can remove many contaminants not removed by activated carbon, including arsenic, fluoride, hexavalent chromium, nitrates and perchlorate. However, reverse osmosis does not remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). Many reverse osmosis systems include an activated carbon component than can remove these other contaminants. Quality can vary tremendously in both the membrane system and the carbon filter typically used with it. Consumers should also be aware that reverse osmosis filters use 3-to-20 times more water than they produce. Because they waste quite a bit of water, they are best used for drinking and cooking water only."[6]


UV (ultraviolet): "These systems use ultraviolet light to kill bacteria and other microorganisms. They cannot remove chemical contaminants. EWG’s water filter guide does not include any filters based on this technology." [6]

Gutters, Pipes, and Downspouts

First Flush

Rainwater catchment systems often include first flush systems. A first flush system is a component of a rainwater catchment system that preserves water quality at the expense of water quantity. These systems work by wasting or diverting the first volume of collected rainwater because of the elevated amounts of solids or contaminants entrained in the collected rainwater. When the first wash of the collection surface by rainfall is diverted or wasted with a first flush system, the collected rainwater contains less solids or other contaminants. Usually, rainwater catchment systems equipped with first flush systems provided safe drinking water as well (Zhu et al., 2004). [7] [8]

Storage

Storage can be either underground or above ground, including cisterns, tanks, and barrels. Container materials include clay, plastic, and galvanized steel. To avoid algae growth tank should be stored away from direct sunlight and should not be transparent. Placement of tank is also important, in order to take advantage of gravitational flow, it should be placed at an elevated area. In order to reduce the distance that needs to be traveled by water, and therefore avoid contamination, tanks should be placed close to area of use. (City of San Diego , 2007) [9]

Materials utilized for water storage can be plastic, fiberglass, or concrete; interior should also be lined in order to make sure that the storage tank is watertight. [10]

[11]

Extra Resources

References

Template:Reflist

  1. 1.0 1.1 Palau Catchment Manual http://ag.arizona.edu/region9wq/pdf/Palau_catchmentmanual.pdf
  2. Shrader, J. A. (2012). La Yuca Rainwater Catchment [PDF]. Humboldt State University. Page 4
  3. WATER QUALITY OF RAINWATER HARVESTING SYSTEMS http://www.pacificwater.org/userfiles/file/MR0579.pdf
  4. http://www.appropedia.org/Practivistas_rainwater_2014/Literature_Review#Roofing_Basics
  5. http://www.appropedia.org/Practivistas_rainwater_2014/Literature_Review#Roofing_Basics
  6. 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 THE NITTY GRITTY OF FILTER TYPES AND TECHNOLOGIES. (2013, February 27). . Retrieved June 8, 2014, from http://www.ewg.org/report/ewgs-water-filter-buying-guide/filter-technology
  7. Kun Zhu, Linus Zhang, William Hart, Mancang Liu, and Hui Chen. Quality issues in harvested rainwater in arid and semi-arid Loess Plateau of northern China. Journal of Arid Environments, 57(4):487 { 505, 2004. ISSN 0140-1963. URL http://www.sciencedirect.com/science/article/pii/S0140196303001186
  8. Shrader, J. A. (2012). La Yuca Rainwater Catchment [PDF]. Humboldt State University. Page 5
  9. City of San Diego . (2007). Water: A Branch of Public Utilities . Retrieved from http://www.sandiego.gov/water/conservation/rainwater.shtml
  10. http://www.appropedia.org/Practivistas_rainwater_2014/Literature_Review#Roofing_Basics
  11. Governor, Bob T., and Nick J. Baird, MD. "Plans for Developing a Rainwater Cistern or Hauled Water Supply." A Markov-Weibull Rain-sum Model for Designing Rain Water Catchment Systems 10.2 (1996): 147-62. Springer Link. Web. 08 June 2014.
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