I wrote in a previous blog post how I’m loving earthbag water tanks. My fascination with these water tanks jumped up a notch after reading an article about the difficulties of building a concrete water tank. From what I’ve recently learned by visiting Vanuatu and assisting in water tank design and construction, I know earthbag water tanks are much faster, easier and lower cost to build than concrete tanks.
How earthbag water tanks are an improvement over poured concrete water tanks:
– No need to build forms and strip them off later. The polypropylene tubing serves as the form.
– No mixing (by hand or with mechanical mixer). Crushed limestone can be used by itself as is if it has sufficient moisture to bind together. (Dry powder won’t bind together.) Concrete uses a mix of sand, gravel and cement. In the referenced article (link below) the lady had to shovel the ingredients into a gas powered mixer and then pour the concrete into the forms.
– The wall material (ex: crushed limestone) is handled only once. Shovel the crushed limestone directly into the tubing or put in a bucket and pour it in.
– Lower cost and fewer materials required. While I don’t have a detailed cost breakdown to present here, it’s pretty clear earthbag water tanks cost less. For starters, you could eliminate the expensive wooden roof structure. A ferrocement top could be $1,000 less. Note how earthbags don’t need a foundation and can last for hundreds of years if protected from UV rays.
– Simpler construction process. Read the article and compare what this lady did with simply filling earthbag tubes in a circle with crushed limestone, tamping them solid and then plastering with cement.
– Stronger and more durable. Compacted crushed limestone gets harder and turns into stone over time from what I’ve been told. Earthbags can last for hundreds of years if protected from UV rays. (My earthbag ebook cites a US Department of Transportation study that tested the durability of polypropylene.) Earth berming large tanks like the author did in the Backwoods Home Magazine is highly recommended to counteract the thrust of the water in the tank. What if you have a leak in 10-20 years? Just add another coat of plaster on the inside.
A telling detail about the durability of concrete made with Portland was mentioned in the magazine article. Here’s a quote: “I say “permanent,” but now I have my doubts after overhearing an old timer at the hardware story drawling to another old timer: “There are two kinds of concrete—concrete that’s cracked, and concrete that’s gonna crack.” Then they cackled and wheezed.” So yes, it’s just a matter of time until concrete will bust apart, unless you use ancient Roman type cement or geopolymer.
Backwoods Home Magazine
Related: Earthbag Water Tank in Mele Village
Interesting fact about cement water tanks: “The calcium content of the cement tank interior neutralizes the acidic rain caught. Water from a ferrocement tank will normally have a neutral pH of 7-8 compared to an acid pH of 3.5 -4 found in other tanks. Acidic water can prematurely corrode surfaces.”
Source: Ferrocement Tanks
Hi I need to contract a n earthbag tank to hold harvested rain water and am also interested to learn how to do the largest possible earthbag tank to hold water for irrigation.
Detailed directions here: http://www.instructables.com/id/Earthbag-Water-Tanks/
Hi, Owen,
What size crushed limestone do you use? In the U.S. we can get 3/4″- and 1″-, etc.
Also, do you think the crushed limestone would work in mesh (Rachel) tubes?
Thanks
You want limestone powder with some small pieces. Buy a small quantity like 5 gallons and make a test earthbag to make sure it turns into stone like blocks. Try different bags and see what works.
You need to do more research on what the final surface the water is up against should be. There are certain health risks. I would have to dig around for the info. Just look it up.
Health risks from the cement or plastic? Maybe different kinds of water react differently? It would be good to know about any major risks.
With a liner, like we use on our tanks (http://velacreations.com/water/water-storage/item/313-cistern-howto.html), you could save a lot with stucco and floors. Just fine sand, earthbags, and a liner. In expensive and super fast.
That’s a good possibility, thanks. I’m aware of your water tank system, but I hadn’t thought of using a liner inside an earthbag tank.
However, a liner seems most appropriate for very large tanks like yours. The earthbag tanks I’m working on are quite a bit smaller. Maybe it’s best to use cement plaster with earthbag tanks unless you build a really big one.
The thing is, the liner comes out way cheaper and there’s less chance for failure. No floor and wall seams to give over time, no costly slabs, no hours of stuccoing tanks. Putting in a liner, even on a big tank, takes an hour. That’s the whole reason we went that route in the first place. Liner tanks are significantly cheaper than concrete ones.
Yes, but cement tanks have advantages. I’d recommend your method for very large tanks in dry areas where you need lots of water for plants and animals. Then a smaller cement tank for drinking and cooking.
Hi Owen- I was excited to read about earthbag water tanks because now I figure I can afford to finally get a water tank going.
Do the bags have to be filled with limestone though? I have clay soil and thought about digging a large hole so that I could sink the tank part way into the ground, and then have soil for filling backs. I also planned to drive rebar stakes through the bags from top to bottom.
What do you think; could I fill them with clay soil?
You could use clay subsoil in the bags but it wouldn’t be as durable as crushed limestone or gravel or crusher fines from gravel quarries. Keep looking around. Sooner or later the tank might develop a pinhole leak that would erode the clay.
Digging into the earth makes it harder to extract the water. But it all depends on your situation. There are pros and cons to each system. Some prefer elevated water tanks for gravity flow.
I think the liner is the deal- would take care of pin holes. I plan a pump for the lower reaches of the tank.
Thanks Owen!