Water cisterns

We're considering putting in a 3k gallon cistern to capture water off the house.  The cistern is a lot of money, the pumps, connecting piping/hoses and gauges all add to the cost, not to mention the hole that must be dug to place it in.  We have a vague understanding that we can do this project for approximately $5k and save no less than $1k in water costs per year.  Obviously this means we're doing right by the planet and our pocket books within 5 years assuming there isn't Any equipment failures before it pays itself off.  What is your experience with this sort of project, these sorts of equipments?  What lessons do you wish you had learned ahead of time?  

I have no actual experience, but I'm fascinated by this subject.
In particular, I'm curious how you arrived at 3k gallons as your cistern size.
I'm sure there's a formula of average  rainfall to usage needs.
Reservoir size a place for wiggle room in cost.
10 to 12  IBC totes could take the place of the hole, but it might cost more in the long run, between space taken up, freeze protection and all the extra plumbing needed.
A lined hole also has very little that can go wrong with it.

Hopefully someone with actual experience will weigh in.

Appropriately winterizing our system was a big lesson for us, especially really insulating our pump/equipment house. Here's a video of winterization efforts.



Other tips...

- Buy two pumps and make sure your pump is accessible so when it fails you can swap it out easily with your spare one. Our first pump started leaking after a year. The company honored its four year warranty but took about six weeks to send me a replacement. Glad I had the spare.

- We now occasionally dose our water with chlorine(bleach). Otherwise, the water develops a faint organic pond odor. We have two 1600 gallon tanks so after a large rain event I'll put a two cups of bleach in the tank we're not currently using and then a week or two later I'll swap feeds and dose the other tank.

- For filtration we use two whole filters and then a Berkey for our drinking water and that works great for us. Designing the system I read about very elaborate filtration systems but I think the best way to keep your water clean is to make sure you have good collection surface(metal roof) and you keep all the four legged animals off of it.

John C Daley also posts some really good information about rainwater collection systems. Here's link to his post about the benefits of rainwater collection    

Does Portland (edit, location changed to Stevenson WA) get freezing temps for extended periods? I wonder if you don't, if you could get a tank that could sit on grade at a point a bit higher than your faucets, and then you can use gravity feed and avoid some cost. 'Off Grid with Doug and Stacy' is a Youtube channel and they do just that in Missouri, they have several big tanks in a barn and all their water is from rain off that barn roof. Then they run the water line underground about 4 feet deep, and then it comes back up in the cabin crawl space to feed everything including a shower. They use full 2" pipes and fittings to avoid pressure loss, and with just a couple feet (like at most 5) of head their water pressure is fine. No aerator sink faucets though, so if you have various 1/4" fittings along the way that flow/pressure would drop a lot.

Assuming Portland has that cascadia dry summer where there's no rain for 3 months, then you could determine sizing based on water needs for that time frame. 3000 gallons sounds right for the national average plus some outdoor watering needs, 33~ish gallons a day for 90 days of no rain.

at Aaron Yarbrough - Thank you!  This is exactly the type of experiential information that we were hoping for.  This winter has been particularly brutal, the worst this little town has seen in about 30 years so the winterization and extra pump are suggestions we'll take to heart.

Are you replacing or augmenting available domestic water (from a well or municipal water system) with this system or do you not have domestic water available?  I'm not sure that I would consider the savings worth it to use rainwater for drinking and other house functions other than irrigation.  The initial build expense as well as the ongoing maintenance (filter media), pumps, etc and not having anyone to call other than yourself when something fails and water doesn't come out of the tap may not be worth the savings.  Also, we have dry years here, if you are replacing the domestic water what happens if 3000 gallons isn't enough to get through the dry months?  Also if this is your only source of water you probably want to think about building some type of redundancy into your system like spare pumps, etc.

We just finished building the collection side of our 7500 gallon system to catch rain off our roof for irrigation purposes only.  We are building a large garden and our house shares a well with 7 other homes, we don't want to be the ones that use up ALL the water, especially for irrigation. We get enough rain off the roof of our metal building that 7500 gallons will be more than enough to get through the dry season here and don't have to start collecting until the end of February so our system stays empty through "most" of the times that we may see temperatures below freezing long enough to cause issues.  That said, if we have water in the tanks and connecting pipes and temps are forecast below freezing we can divert any additional water that may come off the building, wrap the pipes and potentially even use "heat tape" to keep everything from freezing.  We put as much of the piping underground as we could manage to protect it from freezing but the tanks themselves are above ground.  If this system was to be used the entire season we would have had to spend a lot more time and money to keep it from freezing.

My build thread

Good luck with your build!

Do you have a back up plan if you don't get the needed rain fall?  For a modern water user not used to serious conservation that is 1 to 3 weeks worth of water.   For a family of 4 living a modern life and used to water conservation you can get that down to about 500 gallons a week without badly hurting.  So 6 weeks capacity.  Anything below that requires serious conservation and will increase work and or other expenses seriously.     Trips to town to use laundromat, choosing food stuffs that don't require dishes or using paper plates, spit baths rather than showers or baths and more.  If we as a family of 4 were in max water conservation mode we used 50 to 100 gallons a week.  I grew up on cisterns and will list lessons.  We hauled all water from town to fill our cisterns for 40 years.  We owned 4 different active cisterns we used, had one I saw how it worked but wasn't used and did various major repairs or install to 3 neighbors cisterns too.

First someone asked how you size a cistern.  So lets do a bit of math.  Pretend your roof is 1200 square feet measured in the horizontal plane.(side note in 2019 average house size in the US was 2301 square feet so if the house is 2 story that would put the average home roof right near that number)  First step is to divide your annual rain fall by 12 and multiply that times your roof area to get to cubic feet.  Thus that roof gives 100 cubic feet of water per inch of rainfall.  Now mulitply by 7.48 gallons per cubic foot to get 748 gallons per inch of water on the roof.  Thus it would take just over 4 inches of rain to fill a 3000 gallon cistern off 1200 square foot roof.  Assuming you got regular rainfall with no real dry season and wanted an easy modern lifestyle for water that means needing 52000 gallons a year say.  That would mean basically 70 inches of rain fall a year for that roof size.   Can you saw ouch.  Even at half that still too much rain needed in most places.   Basically the goal is a cistern to hold the most water you will get in a single short stretch or rain fall.  So if in their rainy season they at most get 4 inches of rain in the time period they use that much water the cistern would be sized correctly.  Where I am with average of 4" to 6" per year off a 1200 square foot roof that would be oversized most years.  Best year in my 50+ year lifetime was about 11 inches one year.  That year a 3000 gallon cistern would have been under sized.  But that is a really rare year.  The final step is weighing cost vs benefit in the sizing.

First cistern was my parents first home.  1000 gallons, concrete with the concrete top right at ground level.  Had a crack half way up so it only really held 500 gallons.  Covered access hatch with a board cover.  In winter to keep it from freezing to much to be used it was buried in straw bales.  Often got mice and big insects in it.  At times muddy water ran in because it was the same level as the rest of the yard nearly.  When my parents bought the house it had a hand pump that had to be primed with each use coming out of the top of the cistern.  By the time I was old enough to remember my father had run a water line and electric pump under the house and we had actual plumbing.  Biggest lesson here is the hatch needs to high enough stuff can't run in and sealed well enough to keep everything out.  Other lesson is 500 gallons is not enough to be convenient.    We hauled water basically weekly.  If the truck was down or if it was needed for harvest they had to pay someone to haul for us.  One of the earliest electrical actions I knew to take was when hearing the pump sucking air go turn it off immediately.

Second cistern was huge and we move to it..  16 feet deep octagonal with 4 foot flats poured in place concrete.  It was about 23,000  gallons or some such.  Best cistern ever.  While its flat concrete top was exposed it was the highest point around so no water ran in for the most part.  Plywood cover with a big rock holding it so much fewer mice although there were a few thru the years.  Lots of crickets leaked in.  Fairly large hole so easy to work thru when cleaning the cistern.  Big thing was because of its size we never had to worry about it freezing at a level that mattered.  The water might have 6 or 8 inches of ice on top but the water always seemed to get thru it and down into the cistern water.  Another part of this working is because of size we were never hauling water during bad weather.  Because of depth, needed the long extension ladder while cleaning.  Concrete top better for cleaning but always blew, dragged etc some dirt on and in while cleaning.  House was unoccupied for 5 or 6 years and I later heard this cistern fell in.  But it was great while we lived there.

Third cistern was a precast 1000 gallon rectangular cistern that was large and flat.  The box was one half and a large lid with a round snorkle up was the second half.  those 2 pieces where mortared together by the installer.  The snorkle came up about 2 feet and had a small concrete lid that covered it.  As it required 2 men to put the small lid on or off it was child safe.  No water ran in and way more freeze proof for small size .  Outlet line was about half way up the tank and at times froze.(be sure the outlet line is below your deepest possible freeze.)  Was a pain to clean because of how short the tank was.  I had to lay down to get under the roof to clean.  The man hole snorkle was so small that I had to twist my shoulders to even fit down it.  Standing in it on the floor of the tank I was tall enough that my head was above it all.  Hate short cisterns for cleaning.  If I ever build one being at least 6 foot floor to ceiling would be a requirement.  Because the dirt came right up to the snorkel getting in and out with dragging dirt in was a pain.  The one other thing done right here is that it had about a 4" pvp pipe fill tube with a cap.  No bugs or mice leaked here and the snorkle lid could be sealed from cleaning to cleaning so nothing leaked there.  Last I knew this cistern was still working 30 years later.

fouth cistern was the big mistake.  The farm was being foreclosed.  We were building on a shoe string on another property while still trying to earn a living.  I was a HS senior at this point.  My parents got a bunch of concrete block cheap so we dug the hole and poured the floor.  There was a new material on the market at that point called Q bond that you were suppose to be able to dry stack the blocks and trowel this stuff on and have good walls.   First lesson was that it wasn't water proof.  Water leaked out thru it.  Since we did this going into winter we had to haul water often as it leaked out into the ground that first winter.  The fact that this ground is heavy clay was probably the only thing that saved us.   The lid was two flat poured  slabs we set on with mortar.  One had a square 2X lined cut out for the man hole and also a 4" fill pipe with the cap.  We then screwed a weather strip sealed plywood on this Next summer we found a waterproof concrete sealant to trowel on to stop the leaks.  Fast forward a bit and now we find the walls are cracking and collapsing inward.  Cistern inside was about 10 feet deep, 8 feet wide and 12  to 14 feet long and the long walls were cracking in.  So we poured some patches on and a cross brace wall across the middle and fixed the cracks.  At the same time we added a poured snorkle about 2 feet deep around the man hole.  It was a bit over 3 x 4 feet and just over 2 feet deep.  We then buried the top of the cistern in dirt about 18 inches deep.  This gives a nice ledge to stand on that is easily washed clean to work from and sit on up top while cleaning the cistern  Swing your feet out put shoes on but the seating surface and standing surface inside the hole is easy to clean and keep clean.  Fast forward another couple of years and the corner closest to where we unload is caving in likely from compaction of the dirt carrying down to it.  Pour reinforcement and get a way longer line so the trailer doesn't come as close to the cistern while unloading to prevent compaction.  Fast forward again a few years and the walls are beginning to collapse again.  Now the concrete block is somehow rotting and you can crumble some of it by hand. Best guess is the alkali in the soil combined with micro leaks creating efflorescence to destroy concrete.  No white fuzzy stuff shows because of water fills dissolving it.  Finally abandoned the cistern about 15 years into its life.  We then had a choice of spend about $10k to build a satisfactory system or about $10k to get on city water.  Glad to be on city water.  Can still sort of use the hole in the ground if needed for a cistern but it gets worse every year.  Now one other mistake in this was using the wood framework to screw the plywood lid to.  It started to rot away and we had a year where we collected thousands of crickets in the water.(floating dead in the water or sunk to the bottom.  As best we could tell they went down between or thru the 2Xs and in.  Would build flush stainless steel anchors in to screw the lid down to another time.  One other right thing here is the lid for the snorkle is a hinges slightly sloping flat roof.  It makes a great place to put the laundry basket down next to the clothes line that keeps people from driving over the cistern without knowing it.  Now I would build it far stronger another time as a few years ago I came out to find 2 visiting preteens jumping up and down on it.(the apparently like the cracking sounds it was making)  If I were doing that man hole in the lid again it would be bigger though.  You should be able to take the fattest shop vac on the market down it with the ladder at a usable angle in the hole.  The shop vac fits

Now I have also had contact with 3 neighbors cisterns too.  2 of them are being destroyed by tree roots and we can't seem to keep them out.  One is a good poured in place cistern.  The other the top half was poured in place then they apparently dug out the bottom half simply plastered the dirt with thin layer of concrete.  The joint between the 2 halves forever keeps cracking and yearly repairs for decades don't seem to help.  At this point it has 1" size roots that pop up inside between years.  Keep the cistern tree height away or more from trees!  Also I would wrap any concrete cistern in poly or pond liner both to keep roots away hopefully and stop efflorescence damage to the concrete.

3rd one is 2 buried poly tanks that could be used as cistern or septic tanks T'ed together.  They were like 1800 gallons each.  It has only been in a few years and seems okay other than they have to bury them in a straw bales each winter because of how shallow they are.

Now one that was on land we owned at one point but never used had a hole in the side that was filled from an irrigation ditch.  Having visited with the guy who grew up with that cistern.  When there was water in the ditch they didn't use the cistern and dried it up to clean.  In the fall just before the water went out of the ditch they pulled the plug and let the cistern fill from the ditch.  Let it settle a bit and bucket out to use.  Ran out in the winter at which point they shoveled a bunch of snow over it to melt in the spring and melted snow on the stove for the rest of the winter.

I agree with Jason Nault. 3000 gallons is unlikely to handle all of your families needs through the west coast dry period if you are relying on this for all of your water needs. Are you urban/suburban or rural? We are interested in adding more rainwater collection because well water isn't permitted for irrigation purposes except a small 1/2 acre amount and not at all for commercial purposes. At little more information might be useful. Generally speaking to store water costs about $1 a gallon.

Underground cisterns are inherrantly problematic.
That is why plastic septic tanks look like bomb shelters.
They need to be round for a start to resist pressure just like a submarine.
Tanks above ground or in a basement or heated shed are batter choices..

We actually upgraded our system to 15000 gallons this spring and this being a dryer winter for us we never even got them filled this spring, only made it to about 3/4, if we were drinking this we might be in trouble.  The dry season last year lasted about 1 month longer than normal so 7500 wasn't enough for the garden to get through the dry season, this motivated us to add more storage.  3000 wouldn't begin to be enough.

Stacy Witscher wrote:I agree with Jason Nault. 3000 gallons is unlikely to handle all of your families needs through the west coast dry period if you are relying on this for all of your water needs. Are you urban/suburban or rural? We are interested in adding more rainwater collection because well water isn't permitted for irrigation purposes except a small 1/2 acre amount and not at all for commercial purposes. At little more information might be useful. Generally speaking to store water costs about $1 a gallon.

I need more storage. What is the cheapest route I can go to store about 6000 gallons? It would have to be above ground or at best extending 3-4 feet below grade. Is the answer just big plastic tanks?

I just figured while we are all here....

That's what we did, we have 6 x 2500 gallon tanks.

Dan Fish wrote:I need more storage. What is the cheapest route I can go to store about 6000 gallons? It would have to be above ground or at best extending 3-4 feet below grade. Is the answer just big plastic tanks?

I just figured while we are all here....

I think you will find a single 5000 gal tank the best value.
I am sure 2 x 2500 Gal tanks will be a lot more expensive