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Cisterns - DIY and have more water security

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posted on May, 17 2009 @ 06:13 PM
I recently enjoyed a thread by WarrenB, entitled The Coming Water Wars. During that discussion I mentioned capturing rainwater, and some of the considerations a person should take into account when doing so. Also related is a thread by dodadoom, entitled Woman is denied from using rainwater off her own roof!. After that, I had several U2Us requesting more info on cisterns, roof treatments, piping and pumps, etc., so I've put this humble little thread together.

I realize my little drawings done in paint are pretty crude -- believe me, my drawings by hand are worse.
I'm not proclaiming to be an expert, but it's not my first rodeo either. Hope this is helpful.

This is how I've done our water catchment system; I'm not saying it's the best way. It's the way that's worked for us. If you live in Colorado, WHEW! It's apparently illegal for you to capture the rainwater that runs off your own roof. Maybe you should think about stocking up on bottled air.


I have to mention this..... collecting and drinking rainwater that falls through polluted or otherwise contaminated air may be hazardous to your health. In many cases, the captured water can be filtered, however keep in mind the contaminants that might be in your air when setting up a rain collection system.

There are a myriad of water filters out there, portable and otherwise, and in fact there are several excellent threads in the Survival forum. We have a Katadyn that is portable, however mostly we use our Big Berkey for drinking and cooking water, as well as the icemaker. Our air and rainwater are very clear; we drink a lot of water and don't want to take chances. Besides, there is always the potential for frog poop. ewg.

Related to that is your collection surface. I myself would not want to drink runoff from an asphalt roof. Even though any oils tend to stay on the surface and usually one draws from the bottom of the cistern, I think there's still a certain amount of mixing in the tank. Now, roofing manufacturers do NOT recommend this, however it's fairly common here to coat asphalt roofing with an elastomeric paint, such as Kool Seal.

This is admittedly a debated issue amongst professional roofers, as an elastomeric paint will tend to seal the underside of roofing shingles, and if water penetrates above that, it could cause damming above this area. On the other hand, I saw myself after Hurricane Paloma smacked us last November, at least three asphalt-shingled roofs that should have been replaced years ago...... they were in terrible condition, but the owners had rolled elastomeric paint over them, and I believe in all three cases that that was the only reason their roofing didn't fly off in the Cat 5 winds.

Now, as you can hopefully tell in the following diagram, I've made an automatic cleaning system for our collection. Or, more correctly, it's designed to waste the first bit of rainwater that lands on your roof:

link to larger view

How this works is, the first runoff from the roof -- the potentially dirty water -- flows into the lower 3" piping. This piping in my case is 30 feet long. When that pipe is full, the remainder of the clean[er] water then flows up into the upper piping and into the cistern. You only need an inch of differential between the height of the downspout compared to the height of the cistern for it to flow, so it's nice to have it all underground.

The lower pipe -- the dirty water -- is bedded in rock and has three small pinholes on the underside of it. Reason for this is, if I get rain this morning and have wasted that amount of water in the lower pipe, I don't need to waste it again if I get rain in the afternoon, as I presume my roof is still clean. It takes about a day for the water to leak out of the lower pipe.

The water in the cistern is drawn up through a foot valve, which holds pressure and allows water to be drawn up into the piping, but won't allow the water to drain back into the cistern. I've made a small sump in our cisterns, so we can draw up the very last bit of our water if we choose to, and it also makes cleaning the cistern a snap.


Most of the traditional cisterns I've seen have been either poured, reinforced concrete block, or solid-poured concrete.
There are a bunch of prefabricated cisterns, most of which are designed to rest above ground, in sizes ranging from 55 gallons to upward of 10,000 gallons. Cost of these is usually about USD $1.00 per gallon or a tad more for shipping. You can start small, forget the automatic cleaning system I outlined, and simply run your downdrop into a 55-gallon FOOD GRADE plastic drum. Above-ground cisterns operate very much the same as below grade cisterns. You can figure out the volume of a cistern, or figure out the size of a cistern that will hold the volume of water you want using the following Water volume (container) calculator" target="_blank" class="postlink" rel="nofollow">volume calculator


Here's a photo of our two water pumps. The one on top is 120-V a/c and the one on the bottom is a 12-Volt pump. The 12-v pump has a demand switch built into it, and it only comes on when you are using the water, and pressurizes to 45 psi. That's plenty of pressure to run a house or hose or pretty much anything you need.


Here's another of my fractured drawings to explain how the two pumps work:


The 12-Volt pump runs off two 12-v batteries. Those batteries are charged by 5Watt solar PV cell, which is on the roof.

We mostly use the 12-v pump these days, and depending upon which valves are closed or open, I can draw from either of two cisterns, or our well. These little pumps are great..... this particular one came from Northern Tool and they are self-priming and can run dry without damage.

I hope this has been helpful. If anyone has any questions or comments, advice, input, or mutterings, please don't be shy. I fear I've made it seem more complicated than it is.

Water is going to get more and more scarce, I fear. It's the primary limiting factor, IMO that determines where a person goes (or stays) in a SitX. I know many folks that claim they never drink water. hmmph. The average person cannot survive much beyond 3-4 days without water, and at about 8.4 pounds per U.S. gallon (about 3.8 kg), it's difficult to carry what you need. In a SitX, a person had better be able to also find or produce water.

If my verbosity hasn't already worn you out [shameless self-plug alert] there are some related ideas on my thread Take the Water Challenge

[edit on 17-5-2009 by argentus]

[edit on 17-5-2009 by argentus]

posted on May, 17 2009 @ 07:10 PM
Great information! Thanks for taking the time to compile this for us. I will defiantly be doing this at home. What a great idea!Cheers.

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