Rainwater Harvesting: Design, Calculator & Build It Yourself

Discussion in 'Off Grid Living' started by ColtCarbine, Feb 25, 2012.


  1. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

  2. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    Safety of Rooftop/Rain Barrel Collected Water

    Safety of Rooftop/Rain Barrel Collected Water

    As rain barrels increase in popularity, questions about their use have arisen . . . Below is some information gathered from various credible sources (I neglected to ask permission to post their names):-

    Summary: The consensus is that there is not a clear consensus. There are significant and reasonable concerns about using rooftop harvested rainwater for drinking or watering food plants. To paraphrase a famous adage: Caution is the better part of good health.


    You'll have to weigh this information and should probably gather more before making your own choices and decisions. There are many variables to consider, including what part of the country you live in and what your roof is composed of. You can certainly have your water tested, though I suspect that is a costly procedure.

    [Note: If you can send or direct me to evidenced findings specifically about the use of rooftop harvested rain on edible plants by a credibile source, I would appreciate it.]

    From the Minneapolis Star Tribune Fixit column of 04/04/06:
    "...You can't drink the water collected, nor should you use it to water vegetable gardens. It's likely to be contaminated with chemicals and bacteria. But you can use it to water flower gardens and lawns or to wash lawn furniture, cars, etc...."

    From an Environmental Toxicologist with the Minnesota Department of Health (April 2006):
    Thank you for your inquiry concerning a warning you read in the newspaper about the use of collected rainwater for vegetable gardens. My search for data to back up the warnings turned up some useful information, but not all of the answers that you need.

    Rainwater washing off of roofs has been studied to determine the load of contaminants picked up from roofing material. Some rainwater collection systems, intended for drinking water, discard a first "flush" of water off the roof in order to make sure that organic material such as bird droppings do not contaminate collection tanks. The water is then treated for drinking.

    But the contaminants that you could be worried about are the heavy metals and polyaromatic hydrocarbons from asphalt shingles and other contaminants that may deposit onto roofs from air. It appears that contaminants that rainwater washes off of shingles may be a significant source of surface water contamination. The contaminants that are washing off of roofs include zinc, lead, chromium, arsenic, and polyaromatic hydrocarbons. It is similar to what you might collect off of a parking lot.

    It is possible to find data on the amount (concentrations) of chemicals in rainwater from asphalt roofs. However, I was not able to find information on whether or not the levels were high enough to accumulate in garden plants intended for consumption.

    I believe that warnings not to use roof-top collected rainwater for vegetable gardens are taking a precautionary approach. I do not know if the calculations have been made that would determine the extent to which these substances are accumulating in plants. Those calculations would need to be made before the MDH could tell you whether you could safely use the water for vegetable gardens.

    From another website: "When NOT to use a rain barrel for watering: If you have certain kinds of roofing material you shouldn't use rain barrels for watering plants. If your roof is made of wood shingles or shakes that have been treated with any chemical (usually chromated copper arsenate-CCA) to make them resistant to rot and moss, lichen and algae growth, don't water your plants from a rain barrel. Water collected from copper roofs or copper gutters also should not be used. Zinc (galvanized metal) anti-moss strips-usually mounted at the roof peak-also produce toxic chemicals you don't want in your garden. Don't use rain barrels if you have these strips (you may want to remove them), or if you have had your roof treated with moss-, lichen or algae-killing chemicals within the last several years. Note that nowadays there are asphalt shingles on the market which have zinc particles imbedded in the surface. Check your shingle specifications if you have recently re-roofed.

    In addition, general practice is to avoid watering vegetables and other edible plants, such as herbs you plan to use in cooking, with rain barrel water collected from asphalt-shingle roofs. These kinds of roofs may leach various complex hydrocarbon compounds, so most people avoid using water from asphalt-shingle roofs or flat tar roofs on plants meant for human consumption. To date there is no definitive research on the amounts and types of hydrocarbon compounds which may leach from such roofs, though it is common practice to use water collected from asphalt-shingle roofs for watering ornamental plants and shrubs. Enameled steel and glazed tile roofs generate little or no contamination and rainwater harvested from them is commonly used to water vegetables."

    From an urban rainwater collector and rainwater system designerwho works for the Council on the Environment of New York City (April 2006):
    The New York City Water Resources Group is in the process of having the collected rainwater tested at 1 site. Preliminary results show bacteria in the samples which is expected as we do not treat the water in any way. Also slightly elevated lead levels probably from airborne sources. No other contaninants that might be expected from roofing, piping or tanks. More testing will be done this season and hopefully a full report to follow. We have signage on the storage tanks warning not to drink.

    From someone at the Minnesota Pollution Control Agency (April 2006):
    I can kind of see the bacteria angle since maybe bacteria, fungus, etc. could multiply in a rain barrel, but the chemicals are the same ones that are already in the rain runoff. And bacteria levels in runoff, don't get me started. However, there are chemicals in tap water (like chlorine) and well water (like lime) that make rain barrel water preferable for gardens.

    Anyway, I think I would tell this person that a rain barrel is an excellent idea for the reasons that are listed in the Fixit column, but they should take the normal precautions in cleaning their veggies before eating them. You might also advise them to allow the spring rains to flush off the roof before setting up the barrel.

    I personally have two rain barrels and have no compunctions about using them for watering any plant, veggie or not. I did find (especially when we were heating with wood) that the first few flushes of rainwater from the roof in early spring had some soot and I wasn't comfortable using it for watering plants.

    From someone at the Pesticide and Fertilizer Management Division of the Minnesota Department of Agriculture (April 2006):
    Without water quality data I'm not sure what the basis is for these statements of risk. That said I don't think I would drink the water off an asphalt roof but concerns over using that water on vegetables seems questionable.

    From a University of Minnesota Horticultural Specialist (April 2006):
    [paraphrase] The advice of not using rain barrel water in vegetable gardens is sound and precautionary. Such water should not be used for drinking or for vegetables. Until a detailed study can be conducted, the best advice at this time is to use the water for ornamental landscape plants/lawns.

    Additional comment: I do not think there would be enough zinc or other metals in the collected rainwater to be toxic to plants. This is because any of these substances that may be present would be diluted substantially with the rainwater. The main concern with the collected rainwater is if applied to edible plants, there could be negative effects to humans if those plants are ingested. This would be due to accumulation of metals in the plant tissue over time. More importantly, if there are bacteria (E. coli) in the water and then sprayed on edible plant parts, this could also cause human sickness if the plants are eaten.

    More from an Environmental Toxicologist with the Minnesota Department of Health (April 2006):
    I spoke with a stormwater expert from the Minnesota Pollution Control Agency about your question. He, in turn, sent out a request for input to a national and international list serve. He sent some interesting comments back to me today.

    From the University of Connecticut: "Based on monitoring at a site with asphalt shingles in CT, we found very low (mostly ND) concentrations of Cu,Pb, and Zn in runoff from the roof. The roof did not have lead flashing, though. We did not test for mercury"

    From Snohomish County government, Washington: "Galvanized or copper flashing on asphalt shingle roofs should be a concern also. Here in the Pacific Northwest, where moss grows on nearly everything that's not moving, it's somewhat common to place a galvanized ridge cap on gable-roofed houses with cedar shake roofs. Minute amounts of zinc from the cap wash down the roof surface in rain and prevent moss from growing on the shakes. Without the caps moss grows thick on shake roofs here. I assume that if runoff from a 3-inch wide galvanized flashing is toxic enough to kill moss on an entire roof, it could be affecting other plants as well."

    From Volusia County government, Florida: "The adhesive for shingles is now including parts washer solvents. I understand a waste company in Florida picks up the parts washer fluid, ships it elsewhere and then uses it as part of the adhesive for shingles. I am unsure if the company removes the heavy metals, therefore, I would not use the rain water from the shingled roof-but that is my personal opinion."

    I hope that this is helpful. The consensus from web sites and these interactions seems to be that unless the roof is designed with materials and methods intended for rainwater collection, there is a possibility that toxic substances will end up in the water. The point made about the rainwater being toxic enough to kill moss and mildew suggests that it may actually be toxic to garden vegetables if collected water is a primary source of water for a garden.

    From a Physician with the California Public Health Service (March 2009):
    1) In California (and probably across the nation), rooftops are often sites for raccoon latrines. Raccoons leave feces on rooftops, usually where valleys form, or alongside the intersection of walls and roofs. The danger is the Raccoon roundworm (Baylisascaris procyonis), which is a common intestinal parasite in the raccoon. The roundworm eggs are found in the raccoon feces and the eggs develop in the feces -- often surviving for over a year in dried raccoon feces. These roundworm eggs can be found in roof runoff water; an internet search on "raccoon latrines" will give several references.

    2) Many shingles are now made with a mild algicide and/or fungicide. Usually this is a copper compound, but may be a more complex chemical.

    Filter The Water

    If you are concerned about contaminants in your rooftop-collected water, you can build a device to filter water. Visit this website to see one person's project creating a homemade bio-sand filter. (I can't vouch for how "clean" or safe the resulting water is.)
     
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  3. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

  4. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    Last edited by a moderator: Jan 26, 2015
  5. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    Link to Oregon's Water Rights: Water Resources Department Oregon Water Laws

    Some uses of water are exempt from the requirement to obtain a permit. These are called “exempt uses.”

    Exempt uses of surface water include:


    1. Natural springs: use of a spring that, under natural conditions, does not form a natural channel and flow off the property where it originates at any time of the year.

    2. Stock watering: where stock drink directly from a surface water source and there is no diversion or other modification to the source. Also, use of water for stock watering from a permitted reservoir to a tank or trough, and, under certain conditions, use of water piped from a surface source to an off-stream livestock watering tank or trough.

    3. Salmon: egg incubation projects under the Salmon and Trout Enhancement Program (STEP) are exempt. Also, water used for fish screens, fishways, and bypass structures.

    4. Fire control: the withdrawal of water for emergency fire fighting or certain non-emergency fire fighting training.

    5. Forest management: certain activities such as slash burning and mixing pesticides. To be eligible, a user must notify the Department and the Oregon Department of Fish and Wildlife and must comply with any restrictions imposed by the Department relating to the source of water that may be used.

    6. Certain land management practices: where water use is not the primary intended activity.

    7. Rainwater: collection and use of rainwater from an artificial impervious surface (like a parking lot or a building’s roof).
     
  6. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

  7. tacmotusn

    tacmotusn Mosquito Sailor

    Hmmmm, bird poop on roof, hadn't thought much about that. As for the rest, I have a metal roof so all that shingle roof mumbly gobblygook don't mean squat to me. I just today obtained a 425 gallon poly tank (meant to sit in the bed of a pickup truck, - otherwise it probably would have held 500 gallons) for free. I am going to use it to collect rainwater to redirect to plants.;) It was used for this at it last home, and the owner gave it to me when he moved.
     
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  8. chelloveck

    chelloveck Diabolus Causidicus

    Thanks for the water harvesting resources CC

    Thanks for the water harvesting resources CC. There are a lot of interesting practical articles.

    Edit: One way of dealing with contaminants such as bird droppings in harvested water is to install a first flush rainwater diverter. The first flush of water is diverted to a secondary holding tank used for gardening purposes or for flushing toilets. Depending on the contaminant load, tank water is usually safe enough to drink without treatment, but in places where water borne diseases such as cholera are endemic, treating water IS a necessity. In urban areas where air pollution is an issue (particularly near heavy industrial manufacturing) and in areas subject to aerial cropp dusting, using first flush rain diverters would be highly desireable.
     
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  9. tacmotusn

    tacmotusn Mosquito Sailor

    possible post SHTF gravity feed water system

    That 425 gallon poly tank that has the two squared off side recesses that allow it to sit in a pickup truck bed, would allow me to construct a 4" X 6" timber wood frame as a lifting point without stressing the tank. I could sink 4 telephone poles upright around this tank. X brace and beam at the top of the 4 poles to hoist the empty tank up to as close to the top as possible where a 4" X 6" or 6" X 6" platform could be constructed under it. A roof could easily be constructed over as well as tin sides. I am assuming the poly tanks life will be extended considerably if protected from UV damage over time. My present simple pump in a post SHTF senerio could be configured to pump via solar and 12 vdc gearmotor to the tank, or a mechanical configuration using wind power could be harnessed to supply the 12 to 14 inch stroke needed by the manual simple pump assembly. This whole affair could put the gravity feed system tank 10 to 12 feet above the ceiling level of my house. I think that would supply sufficient pressure for the house.
     
  10. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    Make sure you engineer that to support 3,544.5 lbs plus the weight of tank.

    Water weighs 8.34 lbs/gallon. Maybe you already knew this but I thought I'd mention it.

    I bet there might be an engineer to let you know if those 4"x6" would support that. It does not seem to me that would do it but that would depend on spacing and how tall the timbers were.
     
  11. tacmotusn

    tacmotusn Mosquito Sailor

    Thanks for the reminder. Believe me though, I overthink things and drive people crazy before I act. I am constantly accused of overbuilding everything. I may be wrong, but I don't think so on the following; a 4 x 6 as a post with force applied on top has a certain tensile strength before it would splinter and fail. Ditto if used as a 4"wide plank, 6" thick and say supported by 4" on either end. Obviously significantly less force would be required to make it splinter and fail in this way, than as used as a post support. I believe that if that same 4" x 6" used as a plank, but turned to 6" wide x 4" thick, that it will fail at a lesser force (weight applied say with a 6x6" footprint) applied at the center point. Being retired navy, I have been accused of building everything like I am trying to make it Battleship strong. I will be studying old wooden water towers and railroad bridges for some ideas, as well as engineering design of that period. I have some old WWII era Seabee construction manuals around here some place. Seems to me there are some water tower specs in those. Below is an all inclusive CD of Navy Seabee construction manuals.
    .
    http://www.militarymanual.com/milit...s-engineering-logging-sawmill-operations.html
     
  12. chelloveck

    chelloveck Diabolus Causidicus

    Poly tanks make great vertical growing surfaces

    Poly tanks make great vertical growing surfaces with some mesh or netting.

    Use the poly tanks as a vertical growing surface for a passionfruit vine. The vine will last some 3-5 years, it will reduce UV exposure and you'll have several crops of passionfruit. The vine is an evergreen, it will help to keep the water cool, and it may help protect the poly against radiant heat and ember attack in the event of a fire.
     
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  13. Nadja

    Nadja RIP 3-11-2013 Forum Leader

    Tac, I would recomend that on top of the telephone poles, you build your framework out of used railroad ties. They work excellent and will withstand the weight. I don't think 4x6 will be strong enough, especially over time.
     
  14. BTPost

    BTPost Old Fart Snow Monkey Moderator

    Most of the Water Tank substructures, built in Alaska, are done with 3X12 Stringers on Edge, on 12" Centers, with 10X10 Caps on 6' Centers, sitting on vertical Piling on 10' Centers. That will hold any Full Water Tank, including Alaska Static Snow Loads. I am sure Ghrit has the Engineers Handbook and can confirm these figures. ..... YMMV.....
     
  15. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    <center>[SIZE=+4]Water Towers[/SIZE]
    <hr size="1" width="100%">[SIZE=+3]Enclosed Water Towers[/SIZE]
    1STSHINGLESTANKFRONT1. 2stshinglestankfront1.
    3STHORIZ2KTANKFRONT. 4STSHINGLESFRONT1.

    [SIZE=+3]Enclosed Water Towers[/SIZE]
    [SIZE=+1]1 Story Enclosed Water Tower[/SIZE]
    [SIZE=+1]2 Story Enclosed Water Tower[/SIZE]
    [SIZE=+1]3 Story Enclosed Water Tower[/SIZE]
    [SIZE=+1]4 Story Enclosed Water Tower[/SIZE]
    [SIZE=+2]Add a Wing to the Sides of the Tower[/SIZE]
    </center> <center> <table border="0" cellspacing="8"> <tbody> <tr> <td>[SIZE=+1]Shed Roof[/SIZE]</td> <td>[SIZE=+1]Hip Roof[/SIZE]</td> </tr> </tbody> </table> </center> The Enclosed Frame Water Towers vary between 10' to 20' at the base and 12' to 40 ft' in height. The main towers are built of 6x6's for posts and 6x6's for braces. Upper platform is built with 6x joists, 2x decking, 5/8" plywood and roofing. The exterior walls are on the outside of the braces and made of 2x stud construction. Exterior materials can be wood shingles, horizontal siding or vertical siding. You can also mix and match materials. If you just want an observation tower, you don't need a tank, just a handrail. The tower can, however, be designed to hold water tanks up to 4,000 gal. With the Enclosed Towers, you can add intermediate floors and create usable spaces. These towers make a handy solution to storing water for residential or agricultural use. They can provide gravity flow water when needed and the rooms can be used for any number of possible uses. The 4 story version is wide enough to create a 1 car garage door opening. You can have a variety of choices of handrails and can have either a wood or concrete floor. These towers can also be adaped to serve as Lookout Towers.
    The Enclosed Water Towers are designed to the new 2008 International Building Code for 80 mph winds and seismic zone 4 requirements for California, the most stringent. All plans are signed by a licensed California Structural Engineer or Architect.
    <center> 1STVERTTANKSIDE1. 2STHORIZTANKSIDE1.
    3STHORIZ2KTANKSIDE. 4STHORIZ2KTANKSIDE1.
    </center> <center>[FONT=Arial,Helvetica][SIZE=-1]Last Update 1/23/09[/SIZE][/FONT]</center>
     
  16. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    1STLOTSIDE1.
    [SIZE=+3]Lookout Tower[/SIZE]
    [SIZE=+1]1 Story Open Lookout Tower[/SIZE]
    [SIZE=+2]1 Story Sloped V Braced Lookout Tower w/Room & Deck:[/SIZE] [SIZE=+1]
    <small>No. of stories for Tower: </small>
    <small>1</small>[/SIZE]
    <small><big>+ Lookout</big>
    </small>​
    <small>[SIZE=+1]<small>Tower Base Dimension: Approximately 12' sq.</small>[/SIZE]
    [SIZE=+1]<small>Tower Height: Approximately 10'</small>[/SIZE]
    [SIZE=+1]<small>Platform Height: Approximately 12'</small>[/SIZE]
    [SIZE=+1]<small>Platform Size: 14' sq.</small>[/SIZE]
    [SIZE=+1]<small>Member Sizes: 6x6's for posts & diagonals, 4x Platform Joists, 2x Decking</small>[/SIZE],
    </small> Exterior Studs:<small> </small>2x6's @ 24" o/c
    Siding: 1x Horizontal, Vertical Board & Batt, Wood Shingles<small>
    [SIZE=+1]<small>Wind Load: 80 mph (will adjust for your local area)</small>[/SIZE]
    [SIZE=+1]<small>Seismic Load: Zone 4 regulations (will adjust for your local area)</small>[/SIZE]
    [SIZE=+1]<small>Snow Load: 0 psf (will adjust for your local area)</small>[/SIZE]
    [SIZE=+1]<small>Cost: VariesseePrices for Tower Plans</small>[/SIZE] </small>
    <small>[SIZE=+1]<small>Includes: Basic Open Tower, Platform, Handrails & Lookout Room</small>[/SIZE]</small>
    <small>[SIZE=+1]<small>Additional Costs:</small>[/SIZE] </small>Adjust for Stairs, Ground Freeze, Higher Wind, Seismic or Snow Loads. Printing and Shipping.<small>
    </small><small>[SIZE=+1]<small>Changes and Modifications to plans: see Custom Designed Towers</small>[/SIZE]</small> <small>[SIZE=+2]<small>Before You Buy:</small>[/SIZE]
    [SIZE=+1]<small>Check with your local Building Department Jurisdiction to verify acceptance of the plans. Verify whether a permit is needed and whether a local engineer or architect needs to sign them. Verify what the local snow and wind loads are for your area.</small>[/SIZE]
    [SIZE=+1]<small>Check with your local Planning Department. There are often, use, height, appearance, area, material or property set back limits that need to be addressed.</small>[/SIZE]
    [SIZE=+1]<small>Verify type of soil before building. Designs are based on having a suitable firm soil material to build the foundation. </small>[/SIZE]</small><small>[SIZE=+1]<small>See Building Code & Geologic Notes.</small>[/SIZE]</small>
     
  17. ColtCarbine

    ColtCarbine Monkey+++ Founding Member

    I would imagine the above structures would require larger posts without all of the cross braces and shear integrity of sheathing on the outside of the support structure.
     
  18. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Not so easy, you've described what's technically called an "indeterminate" structure. I don't have the software to do it, and forgotten how to manually, Nor do I have the code requirements for loading. Might have some tables of material strengths around if some one wants to run the calcs, but haven't seen it in years. My bag was mechanical, not structural.

    :D [monkeyeating]
     
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  19. Quigley_Sharps

    Quigley_Sharps The Badministrator Administrator Founding Member

     
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