Rainwater Harvesting

Hey folks.  I’d like to spend a little time on resilient water today.  It’s a rich topic, with lots and lots to write about.

Let’s start by talking a bit about rainwater harvesting.

If you live in the US or the EU, you probably associate rainwater harvesting with owning a rain barrel.

Rain Barrel

A rain barrel is a simple approach to rainwater harvesting.  It’s a ready source of water that you can use to keep your garden alive during the watering bans of the summer months.  For example.  The basic rain water harvesting system includes:

  1. A roof (in rainwater harvesting lingo:  a drainage catchment).
  2. A gutter system that allows you to direct the downspout into the barrel.
  3. A large plastic barrel.
  4. A wire mesh (small enough to block bugs) that filters the water.
  5. A spigot and a hose to allow you to water your plants or fill a watering can.

However, the 55 gallons of water (or a little more with the larger models) you can collect in a barrel, isn’t much.  It won’t last you long if there is a serious disruption.

Real Rainwater Harvesting

If you are serious about rainwater harvesting and want to take it to the next stage, you need to  dig into the DIY forums on the topic.   Another option is to head to Australia.  Due to an intensely arid climate, Australians are at the forefront of developing, deploying, and debugging rain water harvesting systems from DIY to the low cost commercial systems.

Since there is such a big market for rainwater harvesting in Australia, there are low cost commercial systems for nearly every advanced function (while there is a commercial market in the US, it seems scattershot, if that isn’t the case, educate me to the contrary).  Here are some examples:

  1. Wire mesh installed over the gutters to prevent leaves/debris from falling into the gutters.
  2. First divert rain heads.  Prevents debris that gets through the mesh from getting into the system.
  3. A first flush system.  The first water that falls picks up dirt/chemicals from the roof/gutter.  Flushing that water improves the quality of what you capture.

And that’s just the capture phase of the system  There’s lots more to learn from places with too little or too much water that we can apply to our efforts at personal and community water resilience.  Permaculture also offers lots of insight on how to construct our landscapes and structures to allow water to work for us, rather than against us.

You can expect to see some these excellent insights in future reports on the topic.

Your always learning more about resilience analyst,

John Robb

* Be careful.  Rules vary by location.  For example:  In Colorado, due to water rights treaties signed a century ago, private land owners aren’t allowed to capture rainwater off of their roof w/o a permit.  So, be sneaky.

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  • pragmatic sustainability

    Not for indoor use, purely permaculture landscape use.

    So Cal gets about 12″ of rain annually, almost all of it in winter. The huge storage is necessary to store the water for the long dry summer.

    Gutters aren’t the expensive part, the tanks are.

  • DC

    Also, got a 900 sq. ft. roof done in something like the Steel Rock Roof for $5000. Maybe not the same product, I’ll see if I can find out what it was.

    • pragmatic sustainability

      I have 4 quotes for stone on steel roofs and the least expensive is $15K for my simple gable roof with a hip and 2 valleys. The others were $20-25K.

      My day job is in construction.

      I think the difference in wages in a high cost area (greater LA) versus anywhere else but NYC or Chicago is the issue.

      Secondly, the contractors were informed of my plan for solar and water catchment so probably thought I was an easy mark with lots of money to “waste”.

  • pragmatic sustainability

    You are correct, the gutters aren’t that expensive. Galvanized would probably run a couple of hundred dollars and copper a couple of thousand.

    I double-checked the cistern price for 1700 gallon NSF low profile (<5' underground) they are about $2,200 each or $8,800 for 4 tanks with tax $9,600, plus freight.


    Installation and ancillary parts will probably run $5-10K, if you can get it built when nosy neighbors and inspectors aren't around. If they find you doing something the codes are silent on they may pull out a God clause, unsafe practices and stop you.

    There are no returns on underground cisterns.

    Then you'd have to pay for off-site storage of materials for 6-12 months while they make up some rules.

    It should be noted that I live in a low code-enforcement city in So Cal. A master-planned "sustainable" place like Irvine would be impossible and the capital cost would be double if the city required full on Civil, Mechanical engineering and water quality testing.

    • johnrobb

      PS, I suspect there are lots of other savings to be had in the design. Lots more to do on this topic. JR


    I’ve always wondered if hot water heater tanks, in a prolonged emergency, could be used as emergency rain barrels. Would the exteriors need a coating of some kind to protect from rust? Has anyone done something similar?

    • johnrobb

      I have no idea. Don’t see why not.


  • http://www.paulcline.com Paul Cline

    Because you’ll need to be storing the water you collect and water has a significant heat capacity think about these resilience opportunities.

    If you store water inside a building with light falling on it, it will store heat in the day and release it later at night. In cold climates it’s like a heat battery. This can be a component of a Trombe Wall.

    If you store water in a large tank you can do heat exchanges. In an underground tank the water will reach a fairly consistent cool temperature, higher than freezing, cooler than summer sunshine. You can connect a heat pump type mechanical system to loop inside the water to provide additional cooling in warm summers and additional warmth in freezing winters. In a commercial setting you can use cheaper evening rate electricity to freeze the water at night and melt it during the day for a reduced cost of air conditioning.

    Often the most resilient thing to do with the water that we can’t use is put it into the ground. The ground is the best water storage device. We put too much of our water into gutters, streets, and storm drains.

    • johnrobb


      Exactly! Excellent systems thinking.



    • http://supak.com Scott Supak

      I’ve actually seen systems in the SW where they use the stored water for cooling purposes. A friend of mine and I worked on a system where pool water was heated using an attic heat exchanger (attics get very hot), and it cooled the attic substantially while heating the pool water. I’ve seen green homes designed where water stored underground is run through pipes under the floor to cool the house.

      All of this assumes that you live in a place where it’s going to rain sometimes, so, as AGW causes more drought throughout the SW, you might want to look into moving somewhere where it will actually rain occasionally.

      • johnrobb

        Thanks Scott.

        Ground loops, aka geo-exchange systems, are amazing. More on that later.

        Just a quick note:

        That technique works at scale too. I was on a panel once with the former mayor of Austin, TX. They used inexpensive wind energy (the wind blows more at night) to freeze a football sized field of ice underground every night. They then used that ice to provide free air conditioning to the entire downtown area (a big incentive for businesses to locate in town).


        • http://supak.com Scott Supak

          Yes, I have heard that story about Austin!

          I have seen a lot of reports about using ice as a cold storage mechanism. Apparently they’re looking into this on smaller scales as a way to replace freon in AC units.

          Kind of the opposite (but the same, you know) is the new molten salt solar facilities they’re expanding in the Mojave, which focuses the suns rays on a vat of molten salt which heats up to hundreds of degrees and stays that way for a long time. They then use the molten salt to create steam to run generators, so you get solar power that runs all the time, day and night.

          • pragmatic sustainability

            Austin style thermal energy storage systems are relatively common in CA.



            CSU Fullerton


            CSU Bakersfield

            CSU San Marcos


            UC Merced

            All of those systems still require a refrigerant phase change material to convert electricity to stored cool.

            Much like the molten salt (stored heat) is used to boil water and turn a steam turbine to make electricity.

            These systems are a long way from resilience but they provide modern energy intensive thermal comfort. regardless of what the climate outside is doing.

          • johnrobb


            Thanks. BTW: Phase change materials really aren’t that complex (i.e. molten salt is basically salt peter) and are relatively benign. They likely scale well too, which implies that grass roots projects for local heat storage at the community and personal level would likely yield very interesting results.


    • pragmatic sustainability

      The thermal mass of water is a benefit we can capture.

      Thermal energy storage is only cost-effective at the University or Corporate campus environment at the residential scale it very far from being cost-effective. Even then it isn’t a sustainability strategy it is an electric rate arbitrage strategy that actually increases total KWh consumed.

      You could do some form of Living Machine with aquaculture to harness the ecosystem service, but zoning codes won’t allow a Living Machine in the backyard.


      It is easier to quickly bury some tanks for rainwater catchment/resilience.

      • johnrobb

        PS: Thermal mass is used to help heat/cool residences in a cost effective way. Not sure what you are talking about. JR

        • pragmatic sustainability

          Correct low to no tech thermal mass is part of any well-designed house.

          However, too much thermal mass is just as bad as too little. Thermal mass has to be “tuned” to the diurnal swings of a specific local climate to provide the 12 hour offset to the peaks and valleys of daily temperature swings within the temperature range that humans find comfortable.

          In the case of water tanks the thermal mass is variable throughout the year due to rainfall and tuning the mass introduces additional engineering complexity. Overly complex systems will probably break down and be abandoned as resilience is forced on us by physical reality.

          I was referring to thermal energy storage in the traditional energy management perspective.


          This technique provides all of the heating/cooling from storage thermal energy, usually in the form of water/ice and is highly dependent on maintaining the necessary >10 degree temperature gradients.

          • johnrobb

            PS. Thanks for the clarification. JR

      • http://www.paulcline.com Paul Cline

        One problem facing resilience at the single family home scale is the size and capital expense of systems needed to achieve significant cost-effective benefits. This is one of the arguments we have in favor of government. To aid us in doing things that work collectively but not individually. Perhaps neighborhood organizations with CC&Rs and programs like LEED for Neighborhood Development can help push the needle towards resilient solutions.

        Also, I wouldn’t dismiss what you call the electric rate arbitrage strategy. For one thing, it more efficiently utilizes existing power generation infrastructure and increases total system efficiency. For another, it reduces the cost to the user of the system, even though it may increase kW consumption. And another, time shifting of energy resources will always be an integral part of energy resilience.

        • johnrobb

          Thanks Paul,

          That’s a big reason why you need a resilient community around you. Going it alone is possible, but it’s costly and reduces your chances of success at every stage.

          If you run across any info/methods on that, let me know.


  • http://michaelgrace.org Mike Grace

    Hey John,

    Love this site and all the great information and ideas that are coming from it. I have 2 technical questions about the site.

    1) Why is there no link to the RSS feed http://www.resilientcommunities.com/feed/ ?

    2) Why isn’t a commenting system like Disqus being used so users can get notified of replies to their comments?

    • johnrobb

      Mike, I wanted to make this an e-mail oriented community. Re: comments. Went with the standard package on WordPress.

  • http://www.EcoReality.org Jan Steinman

    I’m lusting after the wood barrels in the photo. Where did you get them? How much did they cost?

    I make perry — fermented pear cider — and I’d love to keep it in wood, rather than the plastic barrel I’m using now.

    • johnrobb

      Jan. Not mine.

    • http://www.paulcline.com Paul Cline

      Jan, Try searching for “new wine barrels” or “oak wine barrels” on google.

      • http://supak.com Scott Supak

        Try also “whiskey barrels” although we barbeque enthusiasts buy those up for smoked meats.

  • A Bramble

    We’ve collected and lived off rainwater for the past 6 years (until last spring, when drought forced us to haul in water for the spring/summer months). All the water that goes down a drain in the house, goes into food growing beds in the attached south-side greenhouse (our primary heating source – also, 55 gallon sealed water barrels in the greenhouse help regulate the temperature via thermal mass ).

    The house is on a hill and surrounded by a french drain, which dumps the surface runoff into outdoor growing beds. Multiple swales and on- rock dams around the property slow runoff erosion and allow the water to settle into the ground.

    For an excellent example on rainwater catchment in urban/suburban areas I recommend Brad Lancaster’s work in Tuscon (http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/) where he diverted street runoff into growing beds and planted trees along the streets turning a heat sink asphalt hell into something quite nice.

    Keep up the excellent work Rob.

    A Bramble

    ps Rules against harvesting rain? That should be grounds for revolution right there.

    • johnrobb

      A Bramble,

      Thank you so much for the description of your home and the techniques you are using. Will definitely check out Brad’s work.

      John Robb

    • pragmatic sustainability

      Brad’s books are good, he just needs to publish volume 3, Cisterns.

  • http://ming.tv/ Flemming Funch

    A cheap and easily available tank often used for storing rain water is the IBC “tote” tanks, meant for industrial transportation of liquids. 1000 liters ~ 264 gallons. Around $100. I incidentally just got one delivered just this morning, but that’s for my upcoming aquaponics system, as it also is one of the cheapest possible solutions for fish tanks.

    • johnrobb

      Thanks Flemming. That’s a great tip. Did you get one with a wire frame? JR

      • http://ming.tv/ Flemming Funch

        Yeah, it has the metal frame and has an integrated metal pallet. All new, so I don’t have to worry about what it might have contained before. Sold by a garden supply store specifically for rainwater storage. This one has black plastic, which protects against UV and algae formation, I believe. And for my purposes (fish), it helps keep it warm.

        • johnrobb

          Thanks for the additional info Flemming. JR

  • DC

    Cheaper to use one large tank, rainwater diverters can gravity-feed a single tank from multiple downspouts.

    7500 gallon above-ground tank ~$5000 http://www.tank-depot.com/product.aspx?id=123&c=7500

    • pragmatic sustainability

      In earthquake country, the taller and large tanks will attract unwanted attention from building officials.

      Probably rightly so, the cost for seismic bracing for an above ground 7500 gallon tank that when full weighs 120,000 pounds and is almost 15′ high will attract unwanted attention from both neighbors, criminals and building officials.

      What good will large plastic above ground water storage be if an earthquake breaks it and spills all of the water?

      • johnrobb


        Lots of alternative for above ground storage. I’ll share a pretty slick one next week.


  • c.

    You forgot to mention the cheap method of getting large amounts of storage. Ferrocement. http://oasisdesign.net/ is one of the premier resources for both this and greywater etc. etc.

    If you’re serious about resilience you can put a metal roof on your house next time you do your roof. We have a very complex roof on a very old house and the cost of metal shingles versus 50 year warranty asphalt was about a 10% – 15% price difference depending upon the contractor. This gave us the added benefit of a usable 3rd floor as retrofitting airconditioning was impossible without major interior renovations so white metal roof and the 3rd floor is easily 20 degrees cooler on hot days in the summer. Real world experience and measurement.

    • johnrobb

      Thanks C. Have any personal experience with Ferrocement construction you can share? Thanks for the roof experience info. JR

      • c.

        Er, ferrocement is easypeasy. The bathtub I grew up with was ferrocement, I’ve done a few repair jobs on other water holding structures and recently installed a ferrocement bench in that bathtub. I plan on doing 2-3 of the thai water jars (oasis designs book has a nice pattern) around that beautiful metal roof this summer. I’ll try to document. I don’t know what specifically I can offer that isn’t readily available online. Low materials cost, can’t screw up too badly even for a novice, watch your mixing ratios and drying/curing conditions.

        The water catchment is so I can stop the summer water bill for my fruit trees.

        • johnrobb


          “ferrocement is easypeasy” Nice. Have a instructional video that you would be interested in sharing with us? I can package it up with some info/instructions as a resilience micro report.


  • http://easydigging.com/Garden_Cultivator/wheel_hoe_push_plow.html Wheel Man

    Using rainwater is a lot like using PV solar electricity: FIRST you must drastically reduce the amount you use…

    Part of the water usage reduction can be done with more efficient fixtures, but most of it must be done by changing habits and eliminating some uses.

    Only after your water usage has been reduced and your new habits are ingrained should you start designing a rainwater harvesting system (RWH) to meet your needs.

    Be sure to also check actual monthly rainfall data for your location. Do not use the yearly average number for planning. Some areas have radical differences from month to month, and climate change has intensified the extremes of rainfall and drought. Use actual monthly rainfall data for the last 5 years. Build a spreadsheet to backtest against that data (starting storage plus gallons in minus gallons out for each consecutive month).

    • johnrobb

      WM, Another approach is to do it incrementally. Allocate rainwater harvesting to external uses. Ease your way into it. JR

      • http://easydigging.com/Garden_Cultivator/wheel_hoe_push_plow.html Wheel Man

        Very true. I was writing about indoor plumbing usage…

  • rjh

    One source for local regulatory information is: http://www.harvesth2o.com/statues_regulations.shtml

    The underlying legal theory splits the US roughly at the Mississippi. East of there, the dominant rule is “if it’s on your land, it’s yours”, with fine tuning around pollution, and other impacts. West of there, the dominant rule is “water is a shared community resource”, again with fine tuning. It’s more or less scarcity driven for which legal basis dominates.

    You can get a lot of information and equipment leads from parts of the US where collected rainwater is a major home water source. My relatives in Alaska use a roof fed cistern augmented by trucked in water because their location has groundwater difficulties and gets lots of rain and snow. The Florida keys have a similar large number of rainwater systems because groundwater is very limited, and the alternative is desalination or trucking in water.

    In much of the eastern US there are regulations to encourage and subsidize small scale groundwater collection systems. The motivation is primarily surface water pollution controls because rapid runoff brings lots of pollutants, fertilizers, silt, etc. into the surface water. This harms the land (due to lost nutrients, etc.) and harms the water quality. It’s a significant factor in the problems in Chesapeake bay for example. There is a secondary motivation of reducing waste water treatment costs. That is one reason for a strong push toward green roofs in urban areas and permeable pavement for light duty parking areas.

    The situation is quite different in the dry climates.

    • johnrobb


      Thanks for the added insight on that. Makes sense.

      Check out this rainwater catchment for Gibralter. http://i.imgur.com/XlrqH.jpg


  • OWSBuenosAires

    The IBC tanks are approved to transport food, so they should be pretty inert.

    A cheap way to store water underground is to dig a hole and cover the walls

    with thick plastic lining, the hole should be made taking into consideration the maximum

    dimensions of the plastic lining available or the lining sheets can be thermally fused.

    For redundancy you can use multiple layers of lining.

    To make gutters a cheap method is to acquire plastic bottles, cut the neck and bottom off

    and thermally fuse the segments.

    To fuse plastic you need two flat pieces of metal heated to the plastic fusing temperature,

    one method of having the metal reach that specific temperature is to pass a certain current

    through the pieces for a certain amount of time regulating said current with a potentiometer,

    another if to stick the pieces in an oven set to that temperature.

    • johnrobb


      Spot on. New IBC is safe. Used IBC can be tricky even if they disclose prior usage.

      Nice squatter DIY tricks on gutters and plastic fusing.


  • OWSBuenosAires

    Keeping up with the plastic theme, one way to collect water beyond the surface capabilities

    of your roof or even without a roof is again: plastic lining.

    You need to elevate one side of the sheet high enough so that the plastic doesn’t bend down

    in the middle and hold water there instead of letting it slide down.

    This method is specially good paired with longitudinal water storage ground holes,

    putting collecting sheets to both sides of the canal shaped storage hole,

    since it does away with the need for a gutter system.

    • johnrobb

      Thanks OWS, that’s a very simple DIY solution.


  • Steve

    Thanks for posting this! I am in the process of putting together a system now and this couldn’t have been a more timely article so thank you!

    • johnrobb

      My pleasure Steve. Let us know how it turns out. JR.

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