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Harvesting Rainwater - Accepting a Gift from the Heavens
As with so many aspects of our lives in which we harvest and store things for later use, Larisa and I (Bob) have been harvesting, storing, and using rainwater from water tanks for all of our water needs since 1984. We also collect and store the following:
- Fallen trees, as firewood, for home heating, hot water, cooking, and saunas
- Electricity, from photovoltaic (PV) panels, stored in batteries, for all electrical needs, including hot water backup
- Food, preserved by solar dehydration, steam juicing, steam canning, and root-cellaring/live-storage
- Heat, stored in a 2-ton masonry woodstove and in the 30-ton masonry floor of our passive solar, strawbale home
In this sense, we live a lot like the local squirrels. We gratefully accept what the Earth has to offer, work hard for brief periods of time to collect what we need, and we store the bounty for leaner times. This is part of our "just-in-case" mentality, which lies in polar opposition to the modern "just-in-time" reliance on big projects, expensive solutions, and instant, limit-free gratification.
This is a pretty simple concept, it's pretty straightforward to implement, it's certainly cheap if you already have a roof to collect from and can find a recycled tank for storage, and you definitely know where your water is coming from and how much you have to work with. And if you are not perpetually downwind from some huge industrial smokestack, it may be the cleanest, softest, safest, best-tasting water you've ever had. YOU CAN DO THIS!
So many people are connected to municipal water sources and individual wells that they are led to believe that water is in infinite supply. That's far from true, as the news stories on polluted underground aquifers and above-ground lakes and streams make stridently clear. And you've no doubt heard about the climate-change-related droughts occurring in new locations worldwide. So if you're the sort of person who takes 2 showers per day, plus a load of clothing in the washer, and just can't get along without a flush-able toilet, this may not be for you!
Of course, if you live in an area with dairy operations (or with a friendly fire department), you can often hire a milk trucker (or fire tanker) to bring you a 3500-gallon or larger load of water and fill your cistern for a nominal fee. But then you don't get all of the benefits of rainwater. It is just cheaper than drilling your own well. But if you prefer not knowing where your water comes from, what might be in it besides water, or you just prefer the idea of ramming big steel pipes down into the Earth and sucking it dry like your local parasite (fill in the blank here, ours is the deer tick, Ixodes scapularis), read no further!
- The case for using rainwater: (you can download a free PDF file of the complete Midwest Renewable Energy Fair workshop we do on this, including more detailed photos, by Clicking Here.
Why is my water bad?
Some folks have blanched at the notion of drinking water collected from a "dirty, bird-pooped" roof. First of all, birds stay away from our shiny steel roof since it is very bright and often quite hot. And do you really think that underground water is "pure"?
Rain starts with water vapor condensing on a "nucleus " of dust or air-borne bacteria. This falls through the local sky, removing airborne particles on the way down. The Earth's surface topsoil removes some of the dust and bacteria as the water percolates downward, reacting chemically with the local rocks. It forms dissolved, non-chelated (not protein-bound) minerals like carbonates, phosphates, sulfates, and nitrates. And when it reaches the local aquifer (picture a sand or gravel-filled underground pool) it can also pick up contaminants from local wells and septic tanks, seepage from agricultural wastes and industrial/agricultural chemicals, and naturally-occurring poisons such as arsenic, radon, and lead.
As a township officer in Minnesota, Larisa attended a County Township Officer's meeting where a rainwater researcher gave a presentation. She obtained rain sampling data from the State of Minnesota that proved two things we had always suspected:
- Rainwater is far "softer" (fewer dissolved solids) than groundwater
- It is cleaner (fewer chemicals) than surface or groundwater aquifers by a factor of 10 to 1000
- Rainwater is even more clean when collected in very early spring and late fall
Spring and fall is when agricultural activity, with its inherent baggage of man-made pesticides or stirred-up chemical laden soil, is at its lowest ebb. We collect our water from the roof of our 1000 square foot, single story home. The roof is a simple, galvanized steel shed type, found on many agricultural buildings in our area. The shiny surface deters birds and their associated "debris", it is widely available, low in cost, easy to install, it rinses clean easily, and it lasts a very long time.
The ideal rain collection surface is smooth, chemically inert, and in a spot not overshadowed by trees. For practical purposes this would be a stainless steel, standing seam roof, but that material would lack a couple of these virtues (mainly cost). We've seen folks trying to collect household water from metal tile roofs, asphalt/glasphalt shingles, underneath tannin-filled oak trees, etc. They were not very successful!
Before we collect rain, I reach up and use my hand or a stiff, narrow brush to remove any leaves, maple seeds, poplar catkins, or other debris that might have flown in from nearby trees, from the rain collection "gutters", or "eave troughs". Then I push a clean, moistened, terry-cloth towel down the gutter to remove any fine dust or dirt. Our house was built with a simple shed roof partly so that I could do this without a ladder.
We collect rain for household use only a few times in the spring and fall. Waiting for the forecast of a heavy rain, we first let the roof and collection trough rinse in a steady downpour for about 5-10 minutes.
Bob (yes, it's always me!) then sprints outside to the back of the house where there are 3 sink stoppers at the low end of the galvanized trough (seen further below in detail) that determine the water's destination:
- A "water run" (normally a dry ravine, but full of run-off from higher fields in the spring) leading to a nearby pond
- Three above-ground, 1500 gallon, polyethylene tanks to store water for garden irrigation, using pump-pressurized hoses
- An above-ground, 250 gal., stainless "settling tank" which overflows to our buried, 2500 gallon, stainless milk truck tank
This is the settling tank that gives collected rainwater some time to settle the dust that is the nucleus of every raindrop. A 1.5-inch diameter polyethylene "standpipe" in the tank connects to the tank's drain. When the tank overflows into the top of the standpipe, water flows down into our 2500-gallon, stainless steel, main collection tank (seen further down the page). You can also see the other black polyethylene pipes that feed the pond and the 1500-gallon irrigation tanks.
So anyway, during the rainstorm, at some point Bob runs outside and switches from filling the pond to filling the stainless tanks or the big plastic irrigation tanks. On the stainless settling tank, water flows through a very fine mesh stainless filter screen (made for kitchen use as a strainer), then fills the upper (250-gallon) tank, then overflows to the buried (2500-gallon) tank. Water flows from this big, buried, stainless tank to our house by gravity, dropping about a foot in elevation through a 1.5-inch polyethylene pipe (buried 6 feet below the surface), where it reaches the intake of a 12-volt, DC pump.
The pump is a fancy brass-impeller model made to last a lifetime with only motor brush replacement (we bought it used at 1/3 price). But even a cheap, simple, 12-volt, tractor-mounted spray pump will work for several years without problems. The pump pressurizes the water to 35-55 psi (pounds per square inch) for household use. Bathing, laundry, and houseplant irrigation use no further filtration. Cooking, drinking, and dish washing use carbon block filtration at the sinks. The whole process is invisible to the end user; you simply get clean water from a tap, just like downtown!
This photo shows the three sink drain "tailpieces" feeding into the three drainage options. We just move two rubber stoppers around. One drain always remains open. The drilled angle-iron brackets you see protruding from the roof help to support the extra weight of pipes and water at this end of the trough.
Very little soap is needed for laundry, bathing, or dishes since there are almost no dissolved solids to interfere with sudsing. And everything rinses much easier for the same reason, leading to less water use. Over 25 years of drinking and cooking with rainwater while enjoying excellent health sort of speaks for itself.
The 2500 gallons we store for household use is easily enough for 2 people for an entire year, as long as you use a composting toilet instead of a flushable model. To determine how much rain you'd need to fill a tank this size, start with your roof's area. Ours covers 42 by 30 feet, or 1260 square feet. An inch of rain on 1260 sq. ft. is 1260 times 144, or 181,440 cubic inches of rain. There are 231 cubic inches in a gallon, so 181,440 divided by 231 = 785.45 gallons. So a 3.18 inch rainfall will fill our tank (2500 divided by 785.45 = 3.18).
You can simplify the math by figuring that 1.6 square feet of flat roof will yield 1 gallon in a 1-inch rain. To convert your roof's sloped area to flat square footage, just look at how much area or rain it actually intercepts, otherwise known as its "rain shadow". To get the total rain more precisely using three different systems of measurement:
Square feet of "rain shadow" divided by 1.604 = gallons of water in a 1-inch rain.
Square feet of "rain shadow" divided by 1.927 = imperial gallons of water in a 1-inch rain.
Square meters of "rain shadow" times 10 = liters of water in a 1 cm rain.
This series of photos starts with our sheep shed seen from the North side, showing the rain collection gutter below the roof edge. The area covered by the roof is 27' by 23'. The square footage covered is 621 sq.ft. So in a 1-inch rain, 621 divided by 1.6 = 390 gallons. This is all eventually fed to either the above-ground plastic irrigation tanks or to the "water run".
Water flows to the low end of the gutter where a rubber adapter clamps to the gutter outlet and moves into 1.5-inch, black, polyethylene pipe. A 2" by 6" piece of 1/4" "hardware cloth" is rolled into a 2" tube and inserted into the gutter drain to catch debris. But since it isn't as tall as the gutter, it allows water to overflow a clogged screen and continue to fill the collecting tank after the initial debris removal.
The water flows down into two 1500-gallon polyethylene tanks designed to hold "farm chemicals". The first tank, not shown here, collects the water and allows debris to settle. Water can gravity flow through a pipe and valve to the second tank. On top of the second tank (shown here) is a 1/2 Hp AC pump that pressurizes the water, moving it uphill to our garden. The output of the 1" polyethylene pipe is split into additional branches with quick-links for movable hoses with spray wands that we use to irrigate our main garden. The pipe heading left from the tank's top is an overflow that drains to the pond in front of our house.
This was the final output in the main garden, during the 2007 growing season. There is a shut-off at the base of each "watering wand", ending in a fan-shaped spray head. With two wands in operation, the spray reaches out about 10-12 feet. With only one operating, it reaches close to 20 feet.
This was (in 2008) modified to switch from pressure-pumped spray watering to a full drip irrigation system using recycled rubber hoses in each garden bed (1450 feet of hose in individually switched 50-foot lengths). One 1500 gallon tank was placed at an elevation above the garden, connected to the drip system for gravity feeding. The AC pump and 1500 gallon tank was used to store roof-collected water and pump it up to the gravity feeding tank when we need to drip irrigate.
Next (2009) we set things up with both tanks below the garden, with the pump actually pressurizing all of the drip hoses. This gave a more even irrigation flow to all of the hoses and helped to prevent clogging of the tiny slits in the hoses. We figured out that, as long as we had to pump water either way, we might as well take maximum advantage of the solar energy used to pump it! The trouble was that, without a pressure reducer, some of the drip hose ruptured and blew out too much water. And a pressure reducer would have put more strain on the pump, inverter, and batteries.
So (in 2010) we switched back to a couple of watering wands and all is working quite well.
How much do we need for irrigation?
An acre of ground is 43,560 square feet. For optimum growth in our region, we need about an inch of rain per week. An inch on an acre (acre-inch) is 27,154 gallons. so our 0.125 acre garden needs about 3400 gallons to get an acre-inch of rain. When we use the watering wands a typical watering sessions uses about 450-500 gallons from the tanks. This equates to about a quarter-inch of rain. If we do this every other day during a long, hot, dry spell the plants seem to thrive (even though this regimen supplies only about 3/4" per week), they get real rainwater instead groundwater, and we have enough irrigation water for about 18-20 days.
More photos of rain collection:
The sheep shed has a "wing" on the East that continues into a woodshed. The area covered by this roof is 192 sq.ft., and a 32-foot gutter collects this into a 250-gallon stainless steel dairy "bulk tank" to provide water for sheep, spot watering in the garden, etc. In a 1" rain this roof provides 120 gallons of water (192 / 1.6 = 120). Shown is the 4-inch PVC pipe that feeds into a small stainless sink with a window screen stretched across the top. The sink "tailpiece" drains directly into the tank. A 1-inch poly overflow "standpipe" is connected to the tank's drain so that any excess goes into the 1500-gallon poly tanks below it.
This shows our 2500-gallon stainless tank in the process of being insulated. It wasn't buried quite far enough for the 6-foot frost depth we sometimes encounter, so it is first covered with fine gravel, then 2-inch extruded foam insulation. Over this there is a plastic tarp, then a few inches of gravel again.
This shows the final view of the buried stainless tank, with its insulated aluminum access cover sticking up from the gravel. Also shown is one of the 1500-gallon polyethylene tank with an AC pump above it, used for irrigation (before it got a coat of plastic paint to cut light entry into the tank, which can cause the growth of nozzle-clogging algae).
Suggestions and changes we have made:
One change that happened recently is important for any gravity-fed water transfer pipes. The above-ground polyethylene pipe that runs from our house to the 1500-gallon irrigation tanks suddenly seemed to have an obstruction, as the flow from the roof to the tanks was backing up and spilling over the edge of the rain gutter. The irrigation tanks were filling very slowly and if the rainfall rate increased suddenly the water just refused to flow properly.
I noticed that an anthill had formed under the pipe at one point, forcing it upward at that spot. When I tapped on the pipe it sounded like a dull thud on most of the pipe but sounded more hollow at the anthill. I assumed that this must be a spot where a trapped air bubble was restricting the water flow. Drilling a tiny hole to eliminate the air bubble and resealing the hole was a possibility but I figured that when I drained the pipes next fall the bubble would simply reform the following spring when water re-entered the pipe. So I used a shovel to dig out the (now unused) anthill and lower the pipe back to its former level. Then I detached the pipe from the rain gutter and lifted it to pull the air bubble out toward that end.
During the next rain it was clear that the obstruction was gone and the tanks were filling normally. This points out that if you use gravity to move water through a pipe, that pipe needs to either have a uniform slope or be perfectly level throughout its length or you may end up with restricted flow.
Our latest changes (Summer, 2012) involve another irrigation capacity increase due to increasingly common periods of extended drought. We have added this third 1500-gallon polyethylene tank behind our sheep shed. Rain now flows from the collection gutter to 4-inch PVC pipe leading to a removable nylon filter bag mounted in the top of the tank.
At its right you can see a couple of vertical black tubes which are part of a switchable overflow system for this tank, seen in detail below.
The overflow unit connects two standpipes at the top and bottom. Water flows straight from the new tank to the two tanks below it if the valve at the bottom is opened. But if the valve is closed we accumulate an extra 1500 gallons in the new tank. When full, the overflow pipes allow water to flow up the left pipe and down the right one, bypassing the valve.
Without the tiny air hole I drilled in the upper horizontal pipe the new tank could suddenly drain its entire load due to unintended siphoning. That would not be a great idea if I intend to store more water. But since this new tank is also not entirely above the older tanks, about 150 gallons remains stuck in the bottom, unavailable to our irrigation pump when this tank is drained to the lower tanks (from which I pump the water up to our garden). To solve this I simply plug the anti-siphoning hole when I want all of the water to drain out. The remaining water is then siphoned down to the lower tanks for pumping.
The stout steel gate material mounted on fence-posts at either side of the unit keeps our sheep, who love to rub against things when they need to scratch an itch, from tearing it apart.
That's all for now. Happy Harvesting! And if you have additional questions, you can use the contact information found on our Home Page.
Or click the button at the left, click here, or simply e-mail our Secure GMail.com account listed as "bobdowser".