Team BGRZ, rainwater catchment

Directing and capturing rainwater is an ancient science that is still in practice today. In regions where water is scarce during a few or all seasons, maximizing the collection and storage of rainwater is useful.[1] Rainwater catchment systems can replace or supplement municipal water sources which can be expensive, unsafe and/or unreliable. Our group was contacted by Otros Mundos, a local sustainability organization, to design and build three different water collection systems in Chiapas, Mexico. The first location is an appropriate technology demonstration house in San Cristobal de las Casas, the other two systems are in a rural indigenous community. 

Background[edit | edit source]

In the mountainous region of Chiapas, Mexico, the rainy season normally starts around May or early June and continues until late fall.This is opportune for our group as we have had many torrential downpours to test our systems. From late fall to late spring the municipal water is sporadic, and sometimes rationed; for many locals that rely on city provided water, this can be a hard season. For the indigenous community, water is obtained from a local stream. There are at least three months when water is scarce making it extremely difficult for them to obtain water. One of our rain water catchment systems will only be for pig drinking water, gardening water, and washing dishes at the demonstration house and the other is for cooking and cleaning, and possibly potable water in the indigenous community.

Contributors[edit | edit source]

Team BGRZ is made up of four Cal Poly Humboldt students and alumni: Brianna Diaz, Gabriela Pecina Escobar, Robert Duncan and Zach Estela. Brianna is an Art Education/Spanish major. Gabriela is a Spanish Education major. Robert has graduated with a B.S. in NRPI (Natural Resources Planning Interpretation). Zach has graduated with a B.S. in Environmental Science - Appropriate Technology and Climate Change. Project partners are as follows:

  • Otros Mundos
  • Juan Hidalgo, earthen builder and owner of an appropriate technology demonstration house in San Cristobal
  • Indigenous community members

Building Locations[edit | edit source]

  • Juan Hidalgo's Demonstration House in San Cristóbal de las Casas, Mexico
  • Indigenous community in Rural Chiapas

Criteria[edit | edit source]

Weighted Table[edit | edit source]

This table defines and weights the criteria used to evaluate a successful project.

Criteria Weight Constraints
Culturally Appropriate Design 9 Community acceptance, as indicated by communication
Educational ability 6 An Appropedia page where internet is available, also building together with clients and discussing maintenance needs
Level of material locality 6 Local access to project materials
Maintainability 8 Ease of maintenance
Size and location 6 Use appropriate, tank must be out of the way
Cost 10 Affordable for the client
Durability of material 7 Last several years with maintenance
Life Use of rainwater catchment system 6 At least 30 years of use
Reduces erosion 5 Erosion reduction
Local labor and Local skills 9 Project repeatability with local skills and labor
Improves Health 9 Water quality and therefore overall health benefits
Appropriateness 8 Appropriate technology ethos, must have local/reused materials when possible
Modular Design 7 Incorporation of modular design principles, i.e. interchangeable parts
Construction time 9 Four weeks
Replenishment 9 Sized to be replenished year round by average rains

Literature Review[edit | edit source]

Rainwater catchment systems in general have many varieties in construction. Each catchment system installed in Chiapas will have variations in design because each site has specific needs and different sized spaces for the tanks and catchment systems. In this section, we will be discussing rainwater quality, filtering systems that include the first flush, materials used/needed, and system design.

Reasons For Contamination[edit | edit source]

Four main reasons for rainwater contamination are as follows:

  1. Polluted while passing through atmosphere
  2. Filth collected during dry season
  3. Dirty roof, e.g. animal or bird droppings
  4. Pollution through collection unit[2]

Materials[edit | edit source]

Toxicity[edit | edit source]

  • Pvc can be carcinogenic, Greenpeace Recommends Polyethylene (PE) or Polypropylene (PP) as a safer alternative.[3]
  • Zinc oxide, from corrosion of Galvanized corrugated roofing material has a reportedly low toxicity and is considered a 'nuisance particle, unless in vapor form.'
  • Furthermore - If the roofs themselves are made of galvanized steel, a gutter made of the same materials is not a significant increase in surface area.
  • The Journal of Water Research states "The average zinc concentrations in the run-off from the galvanized-iron roof was about 5-fold higher compared to the tile roof, indicating leaching action but was well below the WHO limits for drinking water quality."[4]

Tank Types, Filter Materials, Availability in San Cristobal[edit | edit source]

  • At the demonstration house in San Cristóbal an 1100L tank, unused and located onsite, is employed.
  • A mesh screen attached at a 60º angle and a first flush system are the filtration methods used as the water will be mainly used to water a garden and for cleaning pigs
  • The indigenous community near Acteal plans to build and install 2 ferro-cement 20,000L tanks
  • This system uses both the screen and first flush filtration methods. It also uses a sand filter[5] for extra filtration when the water will be used for cooking and drinking. This filter will be detached from the rest of the rainwater catchment system so that it is only used when necessary, thus reducing maintenance requirements [verification needed].

System Design[edit | edit source]

There are many designs for rainwater catchment systems. The designs vary because of several factors:

  • Roof type, shape and size
  • Tank type, shape and size
  • Purpose of water, ex: garden or drinking?
  • Materials used (budget)
  • Space to put tank
  • Where is tank in relation to roof
  • safety: Will there be kids around? Animals? Is it in a walkway?

Making Rainwater Safe to Drink[edit | edit source]


Rainwater must be kept free of contamination to be safe to drink. To support that water you collect will be safe:

  • Clean the tank, entrance pipe, and roof gutters before the rainy season.
  • Allow the first rains of each year to run through the tank to clean it.
  • Connect a water filter to the tank (slow sand filter is a simple way to do this).
  • Porous beds are part of sand-gravel filters used to clean rainwater. This article has a great photo of a porous bed.
  • Animated video
first flush methods
  • First flush systems are very simple filtration systems to get out larger debris before the sand filter. This helps to keep maintenance to a minimum.
  • The tipping gutter system works by filling up a bucket with dirty water, when bucket weighs enough it will change the direction of the gutter to fill up the storage tank.
  • The floating ball technique functions by having the contaminated water fill up a pipe that has a ball in it. The ball floats to the top as the pipe is fill and eventually seals the pipe so the clean water is diverted to the water harvesting tank.[7]

floating ball demo

Climate Data for San Cristóbal[edit | edit source]

Precipitation Data for San Cristóbal[edit | edit source]


  • According to Rainwater Harvesting Industries, one mm of rain roughly equates to one liter for every square meter of roof surface.
  • Very Concise E-Book called Design for Water : Rainwater Harvesting, Stormwater Catchment, and Alternate Water Reuse Written by: Kinkade-Levario, Heather Published by: New Society Publishers,Call number: Limited TD353 --.K56 2007eb NOTE: must be logged in to HSU library to view this book.

Rainfall Data for Mexico[edit | edit source]

Table 2

This table shows rainfall data for the 10 rainiest states of Mexico in millimeters both by monthly averages and yearly totals

Temperature Data[edit | edit source]

Table 3

This table shows monthly temperature and rainfall data for San Cristóbal, as well as annual averages and totals

Equations[edit | edit source]

See Basic rainwater collection calculations for relevant rainwater collections equations and a rainwater calculation spreadsheet.

Discussion[View | Edit]

Overall Page Feedback[edit source]

  • Good Project Scope introduction, I switched the location of Project Scope and Background, because your Project Scope is so good it should be on top.
  • I added a section called "contributers", and added what used to be the beginning of your background which was just your names and educational background. I also added Otros Mundos, Juan Hildago, and the Majamout community to your contributors section.
  • Great Tables, just give a brief description of any tables you use, at least say how your using the info for your project.
  • some of the Journals and websites in your Literature Review have no description, these lit reviews are not just for looks, we will reconstruct the lit reviews by the end of the program and each team should have the information in the literature review integrated into the other sections of their page like "Materials" or "Project Scope" etc. Please describe what you read don't just write the name of the book and move on.
  • use reference or footnote citation throughout your page, for any assumptions you make. ex: <ref>Smith,Butterfly. "Science Bears". </ref>
  • Section "system design" in literature review needs to elaborate maybe that could be with pictures, but add a bit more description too.
  • In "Equations section", you say "Roof size to pipe size Volume of tank size". Where is the = or / . I dont understand what your saying.
  • Very good writing!

Literature feedback[edit source]

What's the deal with the missing references indicated by question marks? Please either insert the appropriate references in the reference section, or delete the question marks.

Thanks, Tressie 02:20, 9 August 2010 (UTC)

Nice start. Some more english, formatting and journal articles needed.

Some additional suggested topics:

  • tank types configuration
  • tank sizing
  • overflow
  • maintenance/lifecycle cost
  • overview of water utilities in chiapas
  • water prices and origin
  • rainwater quality
  • San Cristobal and Chiapas precipitation
  • Filters
  • Roof types

Additional comments: Use thumb and caption on images. See Help:Images for more. Enter tables as tables and not as images. I made changes and left comments on the mainpage as well. You can use the history tab and compare changes to see the changes.

Thank you, --Lonny 19:49, 18 July 2010 (UTC)

Objective/Background Feedback[edit source]

Nice start, don't forget to reference all assertations.

  • separate some of your info into a "Background" section, the first couple sentences under project
  • scope are perfect. makes sure to back up your statements with references.
  • Change "rainwater catching systems" to rainwater catchment systems.
  • thanks for the otros mundos link
  • last sentence in first paragraph is too informal in its voice.
  • spell out "technology" in fourth sentence.
  • Second paragraph definitely belongs under background.Drop the "Here" from the first sentence
  • second paragraph. back up your climate asserations with reference
  • add a sentence like: "The objective of this project is....."
  • second to last sentence, second paragraph awkward needs to be rewritten.
  • Last sentence is awkward, grammatically incorrect, and maybe redundant, please rework.
  • caption your blackbox image
  • blackbox comment: is potability the only significant need for the collected water? just asking.
  • overall well written but you absolutely need references to back up your background assertations.

--Jeff Hinton 00:43, 19 July 2010 (UTC)

System design[edit source]

Hi Rainwater team,

Great work on the projects.

This document really needs to have the literature review removed and system designs put in its place. Use the literature information to create references for assertions using the ref tag.

Thanks, --Lonny 22:44, 8 August 2010 (UTC)

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