Adventures in Rainwater Harvesting
After losing five important trees to the 2007 drought, the threat of another rain-free summer meant it was time to make a decision about collecting rainwater. Al Cooke, the Chatham County Ag Agent, assembled an extensive list of links about rain collection at http://www.ces.ncsu.edu/chatham/ag/RainHarvest.html . The page offered plenty of information about building or buying barrels, and some considerations about the impact of rainwater collection on the larger water system. However, we didn’t see a lot about designing a whole-house collection system. This article is a record of the process we followed to get our system up and functional. The pictures were taken and added several years later, when we were adding a system to a different house. In revising the article, I realize the economics change considerably when you pay sewer fees in addition to water bills. (Our first system went into a house with a septic tank.)
Volume = Cost
Plenty of websites discuss the issue of “How much can we get?” Allow 700 gallons per inch of rain, per thousand square feet of ground-floor house. This is a lot of water. It doesn’t take much rain at all to fill a barrel or two.
This datum leads to, “how much water do we (think we) need?” which leads almost immediately to, “how much can we afford to store?” (We’ll come back to “How much do we need?” later.)
Collecting and storing water is an expensive proposition. At $10 each, a garden-safe plastic 55-gallon drum provides water storage at $0.20 per gallon. Add plumbing (collection cup, faucet, overflow, connector to another barrel) for $15, and the price of water has risen to $0.45 per gallon. Pre-packaged barrels sell for $50-$95, plus shipping in some cases, and store between 55 and 80 gallons of water, at a cost of $0.90-$1.20/gallon. I pay less than a penny a gallon for water from the county.
However, in August when the county has imposed water use restrictions and expensive trees are showing signs that they’re not going to make it, the relative cost of water changes. Fines. Replacement trees. Dead tree removal. Lost years of landscaping growth, and the thought that next year’s summer may not have any more rain, so replacement trees will die, too. All of a sudden, $0.45 for a gallon of landscaping water doesn’t seem so bad.
Furthermore, the cost of barrels is a one-time charge; they’ll collect water for a long time. And rainwater itself is free.
It quickly becomes obvious why farmers store water in ponds. It’s the cheapest way to store thousands of gallons. (In most cases, pond storage will require a pump to deliver the water where it is needed, so the equation gets complicated.)
Dig a pond if it’s an option. If it’s not, read on.
If you can reduce the cost of the storage system at all, the storage cost falls rapidly.
Our system uses one “collection” barrel per downspout, built with a PVC collection cup to accept water from the downspout and a brass faucet that will allow us to get the water to the garden. We move the water from the collection barrel to “storage” barrels using threaded galvanized pipe and irrigation tubing. Because the inlet and outlet plumbing is the most expensive, a storage barrel only costs $13 or so, rather than $25. We will be able to connect as many storage barrels as we want; our town does not have appearance restrictions.
Piedmont Biofuels Co-op sometimes sells 375 and 250-gallon intermediate bulk containers (IBCs) (square plastic container housed inside a welded aluminum frame) for $100. They did not have any in stock when we started building our system. (We have since found these on Craigslist for $50.)
Volume = Volume, and life and death in August
My water bill jumps about 1000 gallons / month in the summer. I do not know how much water it takes to keep a tree alive. I am planning to measure more carefully this year. I may irrigate using 5-gallon buckets with a small hole drilled at the bottom. Fill the small buckets from the rainwater barrels, then let the water trickle out slowly. I’ll be able to measure both rate of delivery and total amount of water delivered. (I measure things for a living at my day job, by the way.)
I’d like to have at least a 700-gallon capacity, which means we need 14@55-gallon drums. Any brief thunderstorm would help to recharge the system, turning what would normally be water that runs off baked earth into drip irrigation that soaks in deeply.
At some point in a hard summer, decisions will need to be made about which plants get the water. You may not be able to save everything. Thinking about which plants are most important to you is part of the design of the system.
Designing the system
Gravity is your friend
and your enemy. Water is heavy. Gravity is what makes plumbing leak. Gravity is what makes water flow without pumps. A system designed to work with gravity is much easier and cheaper to install and maintain than one requiring any form of pumping.
Consider the relationship of the downspouts to the areas of the garden that will get the water.
In my yard, all of the important plants are lower that at least one or two downspouts, but all plants are not lower than all downspouts. If this thinking indicates you will need to move water uphill, look elsewhere for suggestions.
The Red barrel system is going into a garden that is completely flat. Raising the barrel on cinderblocks will help give some pressure and flow to the water. Four cinderblocks are enough to support the barrel, and set on a concrete pad, they don’t need any support underneath.
/*201211 addition: found instructions for a solar-powered water pump that can increase water pressure enough to use this system to wash your car, or so they say. As yet untested. Radio Shack’s Great Create project provided the instructions. */
Assembling the rain barrel
We studied all the pictures on the how-to-build-a-rain-barrel sites and thought about the hardware we would need and decided to try one barrel first. We connected it to the most accessible spout. A few rainfalls and the barrel was full.
Once we saw what it took to get the water from the downspout into the barrel, we had to rethink our initial design. In the catalog pictures, the barrels sit neatly under the downspout, which runs directly into the barrel. These people do not have electric meters. Or camellias. Or sloping cut-away land right under the downspout. For today, we’re using flexible downspout extenders, mostly because I already owned them. I would like to build PVC connectors in time, but that can wait a bit while we figure out the details. PVC gets expensive, comparatively. (The Red Barrel is collecting free-falling water that drains off a tin roof over the garage. There has never been a downspout at this gutter.)
We used the 1″ drill bit that we already owned; don’t know if a cheaper spade bit would work as well. We also added O-rings to the internal fitting.
(Just realized I didn’t get a detail image of the faucet.) At some point, we may attach a hose to the overflow to carry excess water out into the lawn and away from the slab. For today, the water will run into a 5-gallon bucket that the dogs use as an extra water bowl. The garage roof has been draining to this point for 30 years so it’s unlikely that any more water will make much of a difference. (This is often not the case, and overflow from a rainbarrel has to be directed away from the building.)
The red barrel had a plastic lid held in place by a plastic ring. It was a simple matter to cut a piece of window screen to fit over the barrel (aluminum, because that’s what we happened to have on hand), screw on the ring, and trim the screening. (John is left handed, btw–it’s not a reversed image.)
It happened that we built this rain barrel on a rainy day. Soft rain; no thunder-and-lightning drenching.
We discovered the gutter didn’t drain in the direction we thought. In major downpours, lots of water came out the front, but the back end was open as well and most water drained to the rear of the garage.
In the process of investigating the gutter, we discovered we may have space between two buildings to add up to six additional barrels. Stay tuned.
We collected about a foot of water in the barrel after the first rain.
Tying two collector barrels together
For the second implementation, we addressed the north spout, and this time tied two barrels together. Rather than taking the water around the corner to the driveway, we decided to store it right in the front of the house.
- The barrels are blue, and as such, pretty enough.
- The azalea is evergreen and will hide them.
- There’s a lot of space.
- North side; limited sun = limited algae risk.
- Downside: leakage and overflow will drain into my basement, which is already a water risk. (This is NC: high water table = few basements.) To ameliorate this risk, we decided that each barrel would have an individual overflow outlet, because we couldn’t be sure that a small hole with hose attached would be enough to drain the overflow from more than one barrel under severe rain (= hurricane) conditions. (True enough, an overflow on each barrel isn’t all that much better in a hurricane, but sometimes you just have to do what you can.)
Back to gravity. In order to get both water pressure and enough space under the faucet to attach a hose, you have to raise the barrels. If you put the faucet higher in the barrel so you have clearance for the hose, you’ll lose the use of the water between the faucet and the bottom of the barrel. I’ve seen barrels plumbed so as to lose the use of at least 15 gallons.
Gravity 2: water is heavy, and plastic deforms under pressure. The base of the barrel must be fully supported or the weight of the water will deform the plastic, perhaps past the breaking/leaking point. We raised our barrels on concrete blocks and 2x10x10 PT lumber. Some barrel vendors sell stands. Up goes the storage price…
Gravity 3: water seeks its own level. If you’re daisy-chaining storage barrels (without valved connectors), they will either all be on the same level, or you’ll only store the amount of water between the bottom of the highest barrel and the top of the lowest.
We plan to connect at least six barrels to the two downspouts at the north corner of the house, which between them collect 2/5 of the roof area. Water from these barrels will be used on the dogwoods and crape myrtles in the front yard.
For today, we’re using window screen between the downspout and the barrel intake to collect roof gravel and keep mosquitoes of the barrel. A neighbor with an extensive system told me the only solution that worked for him was to caulk the downspout to the barrel. (As I write, I wonder how he keeps roof debris out of the barrels. Will have to ask.)