Help me save lots of winter rainwater and use it in the summer!

April 27, 2007 9:00 PM

Water engineering question: help me save lots of winter rainwater and use it in the summer!

I live in Seattle, where the winters are very wet and the summers are very dry. I have a large yard and grow a lot of vegetables, many of which (like tomatoes) need lots of water to produce fruit. So my water bills in July / August are upwards of $150 per month. The engineer in me thinks, 'what a waste of resources; I should collect the water in the winter and reuse it in the summer!' The cheapskate in me heartily agrees.

So, I've got my downspout emptying into two rain barrels and one large rubber tub (obtained for free), connected in serial. This gives me 250 gallons of water capacity. A pump sucks the water out of the tub and into an underground watering system where it waters my whole yard (largely though soaker hoses). So far, so good.

However, 250 gallons isn't nearly enough. This summer, I'll probably go through my whole supply in two to three weeks. I'd like to store a minimum of 1,000 gallons. So I've been brainstorming ideas for keeping more water around. Here are some plausible ideas:

1. Buy a bigger tub. Lots of places sell industrial water tanks. But they're expensive, even on eBay / craiglist (used 325-gallon tubs run around $60 -> $120). New, they're about 50 cents / gallon.
2. Build a cistern. Basically, this would be a small underground swimming pool, with a concrete floor and walls, and some kind of lid. Rainwater would flow into the cistern and my pump would pull it out. Even a modest size (10' x 10' x 3') cistern would store 2,200 gallons. However, my construction skills are limited: I can dig and pour a concrete floor, but I'm not sure how to pour walls, or build a sealing lid.
3. Dig a series of holes and line them with pool liner. Use the dirt walls as structural support and the liner to make it impermeable. Basically the same as #2, but simpler to build. Still not sure how to fashion a sealing lid, though.
4. Dig a well, and use a well pump. This is less implausible than it sounds because I happen to live at a geographic low point (near MLK and Union, if you know Seattle). When I dug post holes this spring, we hit the water table less than three feet down. But I don't know how deep it will be in the summer, and I don't know how environmentally dangerous that is.
5. Forget about it, because the county is already solving this problem for me, far better than I ever could, by tapping watersheds and rivers.

Any suggestions? I don't mind doing lots of semi-skilled labor, but I'd like to keep the cost down. I don't care if the water is potable or not; it just has to not kill plants.

posted by molybdenum to home & garden (21 comments total)

Just do what I did--go around the yard digging random holes to plant trees in.

Using this method, accidentally discover the old septic tank that is something like a giant underground swimming pool full of water and, er, 50-year-old "solids".

Pretend like the "solids" have turned in to perfectly safe compost now, re-christen the tank your "cistern", install a pump, and off you go. This thing holds 1000 gallons of water (and "solids") easy . . .
posted by flug at 9:31 PM on April 27, 2007

Any system you build below ground is either going to require a permit or may be illegal. That said:

Unless you're planning on hooking up a pump, the usefulness of #2 and #3 would also depend on how tolerant you are of dipping buckets into the bottom of the hole at the end of summer to get the last drops of water out. That would be too much of a pain in the ass for me.

Just from Googling, you could check out this book on building your own water tank. You could also try looking at old farms in your area and see if any have above-ground cisterns or tanks that they'd be willing to sell for a lesser price.

Worst comes to worst, if you're able to get two or three new industrial sized tanks that will run you about $360 max, right? Consider it an investment--that's at least one summer of water bills saved right there and you'll save far more than that in future years.
posted by schroedinger at 9:37 PM on April 27, 2007

If you hit the local water table at a depth of 3 feet, and can legally drill an irrigation well (you usually need to pull permits with local authorities and register it for monitoring purposes, particularly if it is over a certian flow rate or cassion size), that's your best bet. A water table that high pretty much precludes effective use of a normal underground cistern, since when you empty a cistern sitting in a site with a water table like that, it is going to badly want to float up out of the ground.

If you didn't have that issue, you'd probably talk to septic tank manufacturers, and simply have one of their cistern type tanks set, which is generally just a variant of a septic tank, set up with blocked drainage outlets, and equipped with a pump access hole in its lid. Most places that sell pre-cast septic tanks sell cisterns, too. The dig the hole, deliver the tank on a truck with a crane, and plop it in, and cover the hole. Takes maybe 3 or 4 hours, at a cost of a couple thousand dollars, if no major excavation problems are encountered.
posted by paulsc at 9:39 PM on April 27, 2007 [1 favorite]

"So my water bills in July / August are upwards of $150 per month. [...] However, 250 gallons isn't nearly enough. This summer, I'll probably go through my whole supply in two to three weeks. I'd like to store a minimum of 1,000 gallons. [...] (used 325-gallon tubs run around $60 -> $120). New, they're about 50 cents / gallon."

Your answer lies in the quotes above. You want a minimum of 1,000 gallons, which is about 1.5 months of water, or $200ish worth of water bills (making assumptions on the cost of your other usage). The cost of an appropriate tank would be around $500.

Your investment pays off in about two years. Get it! Heck, get a 1500 gallon tank. That'll last three months, saving you about $300 every summer. That one only takes three years to pay off! If you look at it as an investment, it's almost a no-brainer, as long as you have the initial cost to spare.
posted by CrayDrygu at 10:13 PM on April 27, 2007

In the city limits, you'll probably have lots of red tape to jump through, especially anything that looks like it could be used for sewage or the like.

I live north of you, and I've considered this as well...I think your best bet would be an above-ground tank, situated ina shed or under a roof. There are some excellent online resources: Texas A&M, Texas Water Development Board, etc.

I personally was hoping to try and catch 10,000 gallons, but have since scaled back plans. If you google rainwater harvesting tanks one of the sponsored links has pretty darn good prices. You might want to look into the engineering costs and the material costs of the concrete before dismissing the plastic tanks. I would be willing to bet you'll pay far more than $1000 to construct an underground concrete tank. Plus, a 600 gallon tank is only 4' in diameter, you could tuck it into a garage or a shed pretty easily. The top inlet only needs to be lower than the lowest downspout.

Another option would be to use a pond liner, like you suggest. The easiest way to do this would be to dig a hole about 4' x 8' and however deep you want, and use pressured treated 4 x 4 lumber to line the hole, with half-lapped corner joints which are also pegged with steel rebar. Line the bottom with sand, and put in your pool liner, folding the corners in the prescribed fashion (there are good guides out there for this) and running it over the top of your framework (which of course needs to be pretty level). You could then fashion a lid out of pressure-treated wood--half could be fixed and half could lift off for access. make sure you build the lid sturdily as you know people will walk on it. Don't forget thinking about overflow, etc.

Another option is to simply make the above but leave it open, as a water feature, with the understanding that as the summer progresses, the water level will be dropping. I suspect the aesthetics of this towards late August will not be so hot.
posted by maxwelton at 10:18 PM on April 27, 2007

Oh, and MLK and Union? Based on this last winter, you could simply use your basement to hold the water. I still can't get over that one.
posted by maxwelton at 10:25 PM on April 27, 2007

When I spent a summer at an ecovillage we were building basically a concrete cistern -- there was some vertical rebar, two layers of chicken wire, and we were plastering this by smearing a concrete (mostly) plus straw mixture in behind . This was before I knew jack about engineering, so I can't tell you how they figured out how thick all this needed to be to withstand the water pressure inside. Permaculture is totally about DIY rainwater storage, so it might be useful to find your local experts and ask them.

Have you considered putting it above ground so you don't have to pump the water around your house? I know that this sounds like a terrible idea because, where are you going to put it? But you'll be happy you have a gravity-fed water system when the power goes out. ;)
posted by salvia at 10:55 PM on April 27, 2007

find your local experts and ask them

Seattle Tilth can likely help you, or at least point you in the right direction.
posted by librarina at 11:20 PM on April 27, 2007

I helped make a cistern, we dug a 8 foot square hole and poured the floor, next day we built a form for the walls using 2x12 planks we raised the form as we poured the concrete, by the time we mixed another batch it had set up enough to raise the form, old chain link fence and scrap rebar was free, coal cinders instead of sand, free. A wood deck was built to cover it,
posted by hortense at 12:11 AM on April 28, 2007

Another option is to simply make the above but leave it open, as a water feature, with the understanding that as the summer progresses, the water level will be dropping. I suspect the aesthetics of this towards late August will not be so hot.

Many places have regulations that swimming pools need to be fenced in. Obviously things like decorative ponds don't qualify but there may be a size where something is considered to be a pool. In any event the best bet would probably be a cover.

But I think a well is a better idea than a tank, if that's legal. Barring that a real tank is second best and as the numbers show this can pay for itself within a few years of lower water bills, assuming you can collect enough rain.
posted by 6550 at 12:35 AM on April 28, 2007

Open tanks are a baaaaaaaaaad idea. Without a fountain or some sort of constant water turnover your yard will become a mosquito breeding festival.
posted by schroedinger at 12:46 AM on April 28, 2007

Looking at this table for water rates and this table for sewer rates in Seattle, you are paying $10 to $15 dollars per ccf (748 gallons). You are using at least 10 to 15 times that amount if your $150 bill is correct. That is roughly 10,000 gallons per month. Guess that half of that is for household use. I don't think your 1000 gallon storage is going to put much of a dent into your irrigation needs unless you get a lot of rain in the summer to replenish it, in which case you probably don't need to irrigate. Your 1000 gallon tank holds at best about $20 of water. Spread over three months you are saving only $6.67 per month.
posted by JackFlash at 1:22 AM on April 28, 2007

If you have a water table three feet down, I think a below-ground cistern would be a bad idea (and would be very unlikely to be approved by the permit office). I would be shocked if they allowed you to dig and pump from a well in your backyard, but you could ask. Above ground, you could build it yourself with ferrocement (easy and cheap, but a lot of work) or just buy some big plastic tanks (probably cheaper -- it's what is used almost everywhere in the world except in extremely poor and rural areas). If you get them used, make sure they weren't previously used for nasty chemicals.

But I'd also do some careful adding up of numbers (see JackFlash's comment above), although you may decide that there is an ecological reason to do this, even if the payoff is in fifty years. Either way, do make sure that you know what the cost/benefit bottom line will be, and be realistic.

And, with your current small tanks or with a bigger future tank, make sure they are capped and screened. Otherwise you will be the neighborhood mosquito breeder, and that isn't cool (particularly as West Nile and other diseases continue to spread). Wandering children also periodically climb into (and drown in) open water tanks; you don't want that.
posted by Forktine at 2:39 AM on April 28, 2007

You have water 3 feet down, and still need to water your plants? What's your soil like?
posted by Solomon at 3:26 AM on April 28, 2007

I think wells are illegal within the city limits of Seattle--newly dug wells in the county I live in are required to be at least 50' from any structure, pretty much impossible within Seattle if King County laws are similar.

I meant to mention that an open pool will need to be protected from being an attractive nuisance as mentioned above.

Seattle Public Utilities has some info. And back a few years ago, the city had a pilot program to encourage people to harvest rainwater. You might call the city and see if they have any kickbacks or other incentives.
posted by maxwelton at 3:31 AM on April 28, 2007

Here's an article you might find useful.
posted by The corpse in the library at 7:59 AM on April 28, 2007

Find a used above ground swimming pool on Craigslist maybe. During the warmer months be sure to cover it tightly with a tarp to prevent it from becoming a mosquito breeding pool. That goes for rain barrels too.

If you wanted to go the el cheapo route, an old waterbed can usually be had for nothing. Holes can easily be patched with innertube repair kits. Get rid of the frame and turn the bladder into a reservoir. You should build some sort of enclosure for it so it doesn't take up a king-sized space in your backyard.
posted by JJ86 at 10:11 AM on April 28, 2007

eco sac looks like the perfect solution - it's what I'm planning on doing for my place if the price doesn't scare me off.
posted by jpeacock at 10:21 AM on April 28, 2007

If you are really only using 250 or 300 gallons a month for irrigation, yet running up 10,000 gallons a month in your home, then maybe you should be concentrating on saving water in your home instead. You know the usual. Showers instead of baths, a gallon milk jug in your toilet tank, full loads only in the dishwasher, replacing your clothes washer with a front-loader, etc.
posted by JackFlash at 12:43 PM on April 28, 2007

Check how this is done in Bermuda, where there are no natural water sources and every house roof collects water into basement cisterns. When I lived there in the 50s part of the system was to keep goldfish in there to keep the water clean.
posted by beagle at 2:40 PM on April 28, 2007

I have a feeling that 250 gallons would last less than a week... it's very hard to determine how much water goes into the ground with soaker hoses; with a drip system you know emitter size (gph) and run time. If you really want to get serious with water conservation, I highly recommend switching to drip.
Here are the formulae you need to determine how much water your roof can collect (you'll have to plug in Seattle numbers), and how much water your landscape uses. For quick reference: 1000 square feet of roof will collect about 650 gallons of water per inch of rain, depending on roof material. So for Seattle, that would be something like 20,000 gallons annually.
posted by oneirodynia at 6:31 PM on April 28, 2007