20 January 2008

Rain Harvester Part 1 of 4


We built our rain harvester because we needed more water if we wanted to grow our vegetables to their fullest potential and feed ourselves year round. We live in a big old house that's broken up into a few apartments; altogether, there are six people who live here. Since it's an old house, we've got a well rather than city water. And since we're just up the street from a quarry, the well is shallow. Our landlord lets us do whatever we want on the house's three and a half acres of land with only one restriction: we can't use the hose. So for us, some sort or rainwater collection system was a necessity. We also plan to collect water when we build our own house (that'd be future house) and wanted to take the opportunity to build a practice rain barrel system.

Before we built the rain harvester, we were collecting a minor amount of rainwater via a garbage can wedged under a downspout. This gave us enough water to triage the thirstiest plants and keep seedlings from drying out, but it wasn't fun to make repeated trips though the yard hauling the watering can, and it was a mosquito nightmare. It also severely limited the size of our garden. We wanted to grow a lot of stuff, but with only 55 gallons of water in reserve a large garden was too much of a gamble. Our corner of Pennsylvania usually gets a decent amount of rainfall in the summer at fairly regular intervals, but that's never something to bank on.

When we started seriously thinking about how we could collect water, we came up with a list of requirements to design our system around. We wanted to be able to store a few hundred gallons of water so that we could water our vegetables at least a little bit in the event of an extended drought. We also wanted something relatively cheap: huge cisterns and pre-built barrel systems were out of the question. And because we don't own the house or the land, we didn't want the rain harvester to be a permanent fixture.

So. We decided on a PVC and barrel setup that could be extended in the future. I think similar systems would work for most people because they're cheap, simple, and can be kept fairly small. If you're looking to collect rainwater, here are some things to think about:

  • How much water do you need? Take into account the size of your garden, the water needs of your plants, the typical rainfall for your area, and any plans you might have for expansion. If you grow only a few vegetables or just want enough water to keep your flowers happy through the summer, one or two barrels will probably suffice. If you live in an extremely dry area and want to capture as much water as you can, more barrels will obviously be better. In our case, we get a decent amount of rainfall but our 1200 square foot vegetable garden needs a bit of extra insurance, so we went with a system that keeps nine 55-gallon barrels full most of the time.
  • How much water can you collect? In addition to your area's rainfall, this depends on the amount of area your roof covers. The formula for figuring out how much water your roof can catch is: G = 0.416AR, where G stands for gallons, A is the area under your roof, and R is rainfall. For example, if you want to figure out how much water the roof of your 20x25 foot garage will catch if you get an inch of rain, you'd do G = 0.416(500)(1), and find that you'll get 208 gallons of water. Nifty! This can help you determine how much storage capacity you need.
  • Where is your garden relative to your house? Thinking about this can help you to figure out how to situate your rain harvester. Our garden is downhill from our house, so we can rely on gravity to carry the water through our hose. If you're working on flat ground, you may need to elevate your barrels a good deal to produce water pressure. On a related note:
  • Are you willing to supply power to a water pump? If you need very strong water pressure or if your water needs to travel uphill, it might be necessary to hook up a water pump to your system. We wanted to avoid using power for ours, and we were lucky that our slight downhill pitch gave us enough pressure to use a hose in the garden.
  • What's your budget? You can build a small 100 to 200 gallon system for under $50 and expand it later on. Ours holds about 500 gallons and cost us around $175. It also can be expanded. It's possible to do the same thing for quite a bit cheaper, too—we bought our barrels, but it wouldn't be very difficult to get some for free. We'll get into a specific breakdown of costs in a later post.

And that's the gist of it. We did a lot of planning before we bought any materials, and because of this I think we were able to build a pretty good system. Anyone thinking about collecting rainwater should really think about their needs before making any investment; different circumstances will lead to big differences in water collection systems.

That's quite enough of us for one day. We've got three more posts about our rain harvester in the works. Tomorrow we'll write about different kinds of collection vessels and how to get your hands on them. On Tuesday we'll run through all the materials we used and how we put everything together, and on Wednesday we'll discuss how the whole thing works and how to take care of it. In the meantime, you might want to check out the comments on this recent Garden Rant post, where a number of people shared their water collection requirements and ideas.

12 comments:

Katie said...

Yay! I am so glad you finally shared your awesome setup secrets with the rest of us!

And what's the blog's name gonna be when you own a house? Future House Farm? Has a nice ring to it.

PS - Started Omnivore's Dilemma. Thanks for the info on Pollan!

Katie at GardenPunks

farm mom said...

Wow! What an impressive system!

fastgrowtheweeds.com said...

Okay, now we understand the method to your madness: No Can Use Hose.

Well, this is very interesting, though. And plants respond so much better to rainwater than they do, say, to the contents of my well! (I frankly wondered why the downspouts from the two outbuildings on our property stopped four feet from the ground (seems weird: downspouts are relatively cheap) when I realized the guy had rainbarrels under there.)

The droughts have become so bad there, Australia's government now actually subsidizes homeowners to put in rainwater cisterns. One of my favorite Aussie gardeners, Nada, put one in last year. http://gflora.wordpress.com/

Good series!

Patrick said...

What you have is pretty impressive, but I think no one should feel like they need to start with a system so big, unless like you they have no alternative source of water.

For most people, almost regardless of climate, a barrel or two under the down-spout of their roof gutter will satisfy most of their garden water needs. Most people would be surprised at how small a roof you really need, and how even a gentle rain will fill a pretty good sized barrel. The roof of a shed or greenhouse often works as well as a larger home roof. Even in Australia where there is a drought, systems like this are practical.

I have a garden about twice as big as yours, and I also have to collect all of my own water. My climate is totally different and very wet (Pacific Northwest like), and my garden is below sea level which means the ground is always a bit damp. Since it's a new garden, I don't know how much water I'll need yet, but I'm expecting it to be less than 100 gallons (400 liters). I'll probably end up with 2 or 3 containers, probably costing very little if anything at all.

The Garden Rant post you linked to was discussing systems much larger, complex and more expensive than the average gardener really needs.

One last thing to consider is it's probably a good idea for any system to have at least two different containers. Sometimes you need to empty and move or clean them, and sometimes they fall over or leak. If you have two of them, at least you always have some water if something happens to one.

dlyn said...

That is quite an awesome set up! We usually have enough rain here and our well taps into a huge aquifer, but you just never know what might happen. With a huge veggie garden and lots of ornamentals, we are considering a rain saving system of some kind - yours looks pretty easy to do. Nice little mathematical formula too - great post!

Rising Rainbow said...

Oh wow, that formula to figure out how much rain comes off of my barns is pretty scary.

Meg said...

Katie, maybe when we finally get Future House, we'll have to change the name to Present House Farm. There is a little too much meta-analysis involved there, I think.

I will be curious to hear what you think of the book; everyone I've seen talking about it has a slightly different take it seems like.


Farm Mom, thanks!


El, I've heard other people comment that rainwater brings about a noticeably better response from their plants. I wonder what that's about. You'd think groundwater would have more minerals and things that the plants would like.

Also, thanks for the link! Her garden looks amazing. I get so jealous of those warm climate people sometimes.


Patrick, good points. You're right, most people probably don't need very large systems, at least not right away. One of the reasons we opted for lots of storage, though, is that we can sometimes go a long time with very little rain, so we wanted to be able to store more than what we would typically need in a one or two week period. The weather has been so unpredictable here for the past few years that we don't want to rely on past indicators of rainfall, either. We also have a really good portable water purifier, so in the event that our well dries up (not unheard of) we'd have a nice supply of drinking water.


Dyln, thanks! It was pretty simple to put together, and we were so glad that we had it last year. For a period of about a month we got hardly any rain, and I think our garden would have otherwise been toast! Every time I go back to that formula, it surprises me how much water can come off of a relatively little space. It's pretty cool.


Rising Rainbow, hi! Every time Kelly and I drive by a barn we think, wow, how much water could we get off that roof? You'd need one heck of a barrel!

Aquabarrel said...

Great set up - for other ideas for filtering and diverting water to and away from the barrel set up you might want to check out: www.aquabarrel.com

Meg said...

Hi, Aquabarrel. I think I've been to your site before, and your systems look like tidier versions of ours. Definitely a good resource for someone looking to buy a rain collector.

Vincent said...

My first thought is about such a systems is about getting water from an old asphalt type roof. What chemicals might get dissolved into the water and then become part of the food? If using it for a potted flower garden that isn't an issue.

Kelly said...

Hey Vincent,
Sorry for the outrageous delay in this response. There are some roof types that can leech chemicals into your harvested water. Standard asphalt roofing is not one of those types. The only curious roofing material I've heard of is a teflon coated metal roof. With anything else, all you really need to worry about is filtering off the chunks of stuff. Also you could design a water trap into the system so that the first few gallons are diverted away from your storage area.

Rebecca said...

I love this project! I have eight barrels myself, two each at four downspouts.

Safety of rooftop water is a valid consideration. Besides chemicals from roofing materials, there is bacteria, windblown and bird-deposited. I contacted various experts and posted their responses. While the current knowledge is somewhat inconclusive, caution (and maybe occasional testing?) is the better part of health.

Nice calculations. Anyone wanting to avoid doing the math manually, is welcome to use our online rainfall harvesting calculator.

I also have a FAQ and a detailed tutorial about constructing rain barrels.