*
question: I live outside of Boston and want to install an underground cistern
for lawn watering, car washing, etc. I am looking for articles and information
regarding this and experts or contractors who have experience in this area.
Thanks
David Conklin
Listeners write in about haunted pipes and building-science tomes, and they ask questions about roof venting and roof leaks.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
*
David - You really don't need much of an expert. Though I suspect in your area you will get alot of odd looks. Basically you buy a precast concrete tank (septic tanks typically work good). Bury it in the ground, run your downspouts to it, drop in a submersible pump and you are done. However, around here (Rochester, NY) this would cost you about $2500. This means outside Boston it will cost over $10,000. If this is a historic district, they may want you to lay one up with waterstruck brick, parge it with lime mortar, then wipe down the walls with horse manure to seal any remaining pores. Rinse the tank and install a steam powered pump, or one of those hand pumps that pressurize a large tank...
Sorry to poke fun and ramble. I think it is very honorable to want to do this, but sadly labor, old money, and life in the fast lane make for an inflated local economy that prohibits and sadly discourages this type of conservation.
To know how much water you could collect you take the plan view surface area of your roof, multiply by the seasonal rainfall for the period you would use it, and this gets you a volume of water you could collect.
I have a cistern, but I am demo-ing it for an addition, I put the pump in the creek instead - Indirect with less storage, but functional.
-Rob
*Dave,I am not the contractor you are looking for but I have a suggestion and a couple of concerns that you should keep in mind.First the suggestion. A septic tank may be a pre-made solution. Check with a septic system contractor to see what is available in your area and what one would cost installed.Concerns. Ground water level. All in-ground tanks will float to the surface when the ground level is high and the tank is drawn down. No one knows more about this than septic tank contractors and septic tank pumpers. If this is a problem in your area they will know.Too much water. I assume you are going to run your roof gutter drains to the cistern. A lot of water can come off a roof in a light rain. You need to have a place for it to go when the tank is full.Here is a final consideration. If you are located away from fire hydrants you should consider incorporating a "dry stand" in your cistern. A "dry stand" is nothing more than a pipe into a body of water that has a fitting that will accept the suction hose from a pumper truck. Very cheap insurance. Once your cistern is in your insurance company may give you a discount. Worth checking.
*An underground tank would be the usual approach, but pricey. If want a cheaper approach you could do what landfills do and create a liner. Dig a big hole, line it with 40 to 100 mil polyethylene, place a pump in screened well casing, and backfill with sand or stream-run gravel (avoid sharp edges). The water will be stored in the porosity of the backfill. The porosity will be between 20-30%, depending on how well-graded it is. Ideally, your local soils are suitable for backfilling (minimal fines and no sharp edges). For 10,000 gallon capacity at 25% porosity you need 40,000 gallons of soil or 180 cubic yards.If the soils can be moved for $8-10/yard you could create your water storage for $2,000 w/o pump. Or 20 cents a gallon which is much less than the typical $1.00/gallon for steel or concrete tanks.If you only need 500-1000 gallons, I like Rob's septic tank idea. Widely available and contractors who know how to do it. Good Luck. -David
*
I have looked into an underground irrigation system here in California. We buy water by the miner inch. I need 2 1500 gallons tanks
Go to a septic tank casting company get them to cast a well housing and in the surface of the top. They will also cast bolts for 2x4 framing if you want to put a building on it. Tell them you don't want baffles this is not for septic system. Out here they are $680 plus 3 hours at $65 for installation. They will slug up so make sure you have some way of removing the material the accumulates in the bottom.
If you have more question let me know.
*
I used "Septic Tank" as a generic term to referr to a precast concrete underground storage tank. In fact I have installed pre-cast box culverts with end caps to create an underground tank of 20,000 gallons. Kistner concrete is big in our area, they have lots of different tank sizes.
I am surprised that you guys don't agree that this is a cost-prohibitive project. The area in question has construction costs in the neighborhood of 4-6 times my area. The concrete tank would probably cost $6000. I don't know what the water rates are in David's area, but this is clearly a cost/benefit type question.
For example - in my area water is $2.00/1000 gallons. If I spend $2000 on the installation and assume a 20 year lifespan, neglecting inflation I better move 50,000 gallons per year through this tank. There is also the cost of pumping this water that we have not yet discussed. Bottom line - I put the pump in the creek.
David can easily buy empty barrels, 1 per downspout for $6 each. Assuming 4 downspouts he's got 220 gallons of storage for $25. Then you could set up a cascade-fill system, a little hard piping and....
-Rob
*I think David needs to take everything we have provided into consideration and then he needs to talk to a contractor in his area with the equipment and expertese to do what he wants. Once he has some figures in hand he can make up his own mind about cost and benefits. He may be on a low producing well or subject to summer time water rationing, or other factors we may know nothing about.
*
I was wondering what kerryw meant when he wrote the storage tank will eventually 'slug up'. What does that mean? Does the water generally stay in good shape, or does it have to be shocked every once in a while?
I'm considering installing one also, mainly for irrigation but the post about the 'dry standpipe' idea makes alot of sense.
If I could take things a step further, what are the pros and cons of having a grey water system from the house connect up with this storage tank?
*
cs: Any sediments from rainwater off the roof or ground will collect in the the bottom of the tank. Another adavantge of a septic tank - they already have provisions for being pumped out. Pros of adding gray water - a more uniform flow and adds volume even during a drought. Cons - rainwater is higher quality (very low dissloved solid, very few chunks) compared to gray water. Why degrade the rainwater? Gray water is a lot harder to collect than rainwater. Rinse but not wash cycle of the washing machine. Sinks and tubs, generally but not toilets or disposals. You'd have to replumb the whole DWV system (and never tell the inspector). Whereas rainwater collection is just some PE pipe to direct the downspouts to your cistern.
Cost effectiveness: Very few situations would justify the expense on purely economic terms. You'd have to want to save the planet, live off the grid, have bad local water, have landscaping that water rationing doesn't allow, need the security of fire protection water, or be a Y2K wacko to justify the expense. But haven't we all included features and details in our own homes that give us satisfaction beyond the money involved? I get more excited about an efficient heat recovery system than a Corian countertop. -David
*Just for the record, When digging for the footings of a new addition we found the remnants of an automatic sprinkler system. The retired neighbor wandered by (old men love to watch young men dig) and told us that the previous owner had the sprinkler system installed. After the first month's water bill of a thousand bucks, he decided that he'd rather let the rain take care of the lawn. He had the thing disconnected.A thousand bucks seems unbelievably high, but even if he misplaced the decimal and it was a hundred bucks, that's pretty steep too don't you think? A cistern may pay for itself in this instance.Isn't it like 6 or 7 gallons per inch rainfall per 100 sq ft of roof area?Dan
*A few more tidbits besides what's already been covered: 1) new money is more responsible for old in the price inflation in the burbs of major cities; 2) problems with above ground barrels include algae growing (picture a swimming pool without chlorine), mosquitoes breeding, (both somewhat aleviated by covered barrels), aesthetics and either drawing from them separaterly or tying them altogether to a pumping system; 3) if you're in a watershed area any excavation for buried tanks may require permitting; 4) concern about other stuff underground (utilities, tree roots that if damaged affect tree health, etc).
*Dan: I had water bills of $100/month in Seattle (!). In part because sewer charges are based on water usage. So eliminating outside watering would have cut both a lot.There are 231 cubic inches in a gallon. So 100 square feet x 144 sq in/sq ft x 1 inch of rainfall / 231 cu in/gallon = 62 gallons. A 1,500 sq ft foot print house would yield 935 gallons per inch of rainfall. -David
*My understanding of grey water systems is that you don't want the water standing around for any length of time (eg days). Even just from showers and laundry, grey water still has some bacterial nasties in it that can turn a storage tank into a septic tank after a short period of time.
*
SLUG is sludge. (I can't spell) Dust that settles on the roof during the non rain periods. Stuff that will go down the drain with the rain water. It will build up.
My neighbor has a gazebo build on his irrigation tank. Under one of the bench seats is where all the mechanical "parts" are. A nice touch to a spectic tank.
I will add another point of where are you going to put the dirt you take out of the ground where then the tank is going?
*
Thanks David,
It's been a while since I've thought about gathering rainfall for my water usage. When I lived in my little cabin off the grid I thought about it quite extensively.
I had a system designed for a residential house on the grid to be self sufficiant in power and water and you only needed about eight inches per year (avg rainfall in Missoula, MT). Six seemed vaugely familiar and I guess I was just too lazy to stumble through my notes. 62 definately rings that bell. Factor of ten again...
A hundred bucks a month in Seattle?! As I remember there's quite a bit of water there. Does it all get sold to L.A.?
*Science experiment for the kids: Put a bucket under the downspout and let it collect sediments (or scoop some sludge from your rainwater cistern). Use a magnet to pull out the iron bits.If there a very little bit of iron, it's from iron-nickel micrometeorites that are coming thru the atmosphere and falling to earth. If there's a lot of iron, your gutters are rusting. -David
*
question: I live outside of Boston and want to install an underground cistern
for lawn watering, car washing, etc. I am looking for articles and information
regarding this and experts or contractors who have experience in this area.
Thanks
David Conklin