Off-grid water filtration

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Off-grid water filtration

Post by conwy » Tue Jun 05, 2018 1:44 pm

"Water water everywhere, but not a drop to spare", as they say.

Given the concerning increase in water shortages around the world, including countries like Australia (where I'm from) I've been investigating ways of collecting drinking water off-the-grid.

First there are solar stills which look cheap and low-maintenance. If some YouTube videos are anything to go by, the setup could be as simple as a collection of plastic bottles glued together, tilted upright, with a bit of seawater in the lower half. Unfortunately these probably wouldn't work in very cold and/or without lots of sunlight.

Another option seems to activated carbon. I haven't looked into it much. It seems like something that would have to be manufactured rather than something you could make on your own. So perhaps not really off-the-grid. However, perhaps with a large enough stash of the stuff, one could survive long enough to find water some other way.

Perhaps I'm being a bit extreme here, and water scarcity isn't that big a concern. Or perhaps there are bigger or more immediate concerns. But it does strike me that water is pretty important, given humans can't survive more than a few days without it.


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Re: Off-grid water filtration

Post by jacob » Tue Jun 05, 2018 2:21 pm

First we have to distinguish between filtration and purification.

Filtration removes particles which is done by running the "raw" water through a series of increasingly fine filters, e.g. gravel, sand, fine sand, and activated carbon. Activated, BTW, just means that the carbon (charcoal) has a large surface area. You can make charcoal by heating wood in a tin can without much access to oxygen. Then hammer it to pieces and you got "activated carbon".

Purification means removing everything from the water except the water, so bacteria, vira, chemicals, etc. Typically this is done via reverse osmosis (you can buy water makers for boats that'll turn saltwater into pure water... they're expensive) or distillation. You can also do this chemically with things like iodine or chlorine.

In general, you'd filter before you purify.

For actually getting water, some people construct catchment systems for their roofs ... which is essentially a fancy way of saying they route a downspout into a barrel. One problem with this is that birds shit on roofs... also pollution (from people's cars and general industry) also fall down on roofs and get concentrated this way. Thus this water needs to be purified. This, of course, presumes that you're receiving regular rainfall. However, 1" on a 1500sqft roof is 935 gallons which is quite a bit! Interestingly, doing this is illegal in some locations as you might not own the rain that falls on your land :o

Water scarcity will be a problem in this century. Lots of water is currently being mined from fossil reserves. However, water is currently so cheap that humans are wasting it left and right. As long as you can afford to pay a higher rate than the city can for its park fountains, you'll be good. If you want to check out ground zero for these issues, see what's going on in Cape Town. Biggest concern here is that while humans can get away with a few gallons a day, if you add in all the water being used for food production and industrial process, a westerner uses closer to 100gal per day. With less water and more people, ... well, you can see where this goes ... so at some point there will be some forced degrowth either in population, industrial intensity, or both, not necessarily evenly distributed. Water shortages will become a much bigger issue in Los Angeles than in Chicago, for example.

If nothing else, it seems like a very good idea to keep at least 1 week's worth of water in the house in case there's a storm or the water supplies get contaminated. If you want to start purifying at home, a Berkey system is widely recommended. You'd still need to filter the water first insofar you're taking it out of the river or somesuch.

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Re: Off-grid water filtration

Post by Stahlmann » Tue Jun 05, 2018 2:25 pm

Asked this question before here, but nothing interesting was posted :p

So started my own research...

According to Youtube university activated carbon doesnt do the job or only do for first part of filtration.

Current conclusions:
Vaxxed against local shite
Antiviral/antifungal/antibacterial medication in the bag
Powder or tablets with ... ocyanurate
Yep, after google-fu it seems there arent any long term research with this compound, but they sell it anyway...

:facepalm: ... rification

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Re: Off-grid water filtration

Post by 2Birds1Stone » Tue Jun 05, 2018 4:12 pm

Jacob, how well do one of those "lifestraw" or "Sawyer" filters work at taking regular water from say rainfall, river, lake, etc, and making it potable?

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Re: Off-grid water filtration

Post by jennypenny » Tue Jun 05, 2018 5:01 pm

@2B1S--Sawyer filters are better than Lifestraws and are easy to carry around. Some people I know swear by MSR Guardian purifiers and say they are more effective. It's always good to do a quick DIY filter first if you can so you don't 'use up' the good filter too quickly. If it were me, I'd boil anything resembling pond scum before filtering. Don't boil anything that might contain chemical contaminants.

@Stahlmann--Regarding filtering: activated charcoal filters are great at filtering out most things. Again, pre-filtering nasty water will extend the life of the charcoal filter. I have a Crown Berkey sitting on my counter that we use for all our water needs. You can get extra filters for them that will filter out fluoride and arsenic if desired. You can DIY a charcoal filter, but they aren't perfect and probably work better as pre-filters unless you're really stuck.

@Both -- Neither is guaranteed to filter out all chemical compounds that might result from a spill or Erin Brockovich situation. They have been shown to remove BPA so maybe they would, but manufacturers advise against relying on them for that. I haven't seen any studies on whether they filter out opioids, hormones, etc.

The difficulty in filtering out chemicals is why rooftop catchment systems can be dangerous. Chemicals can leach from roof materials, and if the rain is on the acidic side, then it might be more reactive causing even more to leach off. You could design a system to lay over the top of the roof that doesn't contain anything harmful (even if it only covered part of the roof). A green roof might work. Stringing a tarp or sail between trees and angling a corner down into a barrel will catch a lot, too. In a pinch, you can set out open garbage bags, pots, coolers, and other containers during a downpour.

There's a big difference between grey water and drinking water needs. In a prolonged emergency, I would probably use a DIY system to filter water for washing (people, clothes) but use pristine filtered water for dishes, consumption, tooth brushing, etc. When you stockpile water, use a two-tiered system so you don't 'waste' potable water on things that don't require it.

edit: It's really helpful to know what contaminants you'll be dealing with. If you know you will use a roof catchment system as your first backup and water from the local river as your second backup, do a trial run and test the water before and after filtering to see whether those are viable options. If you regularly travel or hike somewhere, search online or check recent water quality tests for that area (always available online by law).

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Re: Off-grid water filtration

Post by 2Birds1Stone » Tue Jun 05, 2018 5:37 pm

This is a fascinating topic because I plan on thru-hiking the Appalachian Trail and that's the primary way of cleaning your drinking water.

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Re: Off-grid water filtration

Post by Riggerjack » Wed Jun 06, 2018 9:15 pm

Water filtration and purification is pretty well established tech in Wells and public systems, but you can do it cheaper.

Think downspout to storage barrel to filter barrel to filter barrel to finished storage tank. Now all the water in your storage tank is filtered, you can pull from this for your purified water needs.

Filters and purifiers are chosen based on contaminants. Remember most well owners have been dealing with contaminants on their own for ever. So look to the local well owners for preferred solutions. Here in the PNW, with plentiful rain, a metal roof, in the woods, I have 3 barrels, unfiltered, that I use for landscaping irrigation. If I wanted to use that water myself, I would first run it through a sand filter to remove pine needles and other dirt. Then through a greensand filter, I would set it up to back flush to clean the filters. And let it run like that a few years, to verify that it was consistently able to deal with storms, etc.

Only after the filtration system is working, would I worry about purification. And I would test the water in the filtered storage tank to decide what purification system to use.

But you are in Oz, so you should already have plenty of local examples to work with, from the stories I have heard.

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Re: Off-grid water filtration

Post by enigmaT120 » Thu Jun 07, 2018 9:52 am

I don't purify my spring water. Would collected, filtered rain water be worse? At least my spring water is protected from direct bird poop.

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Re: Off-grid water filtration

Post by Riggerjack » Thu Jun 07, 2018 1:24 pm

Yeah, my best friend's mom still runs a gravity feed system from a spring. His stories of things found clogging that pipe are... Good for drunken campfire stories, but would make city folks run in fear.

I have lived off of unfiltered streams for about a year, I had no problems, but I wouldn't recommend it to anyone not young and healthy.

But each time this subject comes up, someone worries about contaminants from the roof surface. If you are squeemishness, skip to the next post.

Most municipal water systems start with a reservoir, filled full of fish, ducks, amphibians, and their waste. Then it's piped to a treatment center, filteration, and chemical purification added, then piped to your house. Clean, sweet, pool water, right?

Well, not exactly. Visit your state Dept of ecology, look at their fines, and you are likely to find the state fining local water systems for things like: storm causes overflow of sewer system into water supply. Add more chemicals, and keep pumping. Or that some construction company is getting fined for dumping paint into the water systems. And even if none of that horror show we're going on, pipes have evolved over the years. Many water systems are still using hollow log piping. Everett WA just got around to replacing some of theirs back in the 90's. Most municipal systems would only replace them when the leaks were so bad the water was washing away the road bed, causing a major road project to get to the water pipes.

What's that? You never heard of hollow log piping? Google it, then tell me how worried you are about contaminants from the roof.

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Re: Off-grid water filtration

Post by jennypenny » Mon Jul 16, 2018 6:26 pm

Lifestraws are on sale for $9.99 during the Prime Day sale on Amazon.

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Re: Off-grid water filtration

Post by OTCW » Mon Jul 16, 2018 7:23 pm

I've worked in the water and wastewater industry, both public and private sides for my whole career of 24 years. What all the home filters miss on imo is follow up testing. Municipal water systems for average size cities can do hundreds of thousands of tests per year at their plants and in their distribution systems.

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Re: Off-grid water filtration

Post by vexed87 » Tue Jul 17, 2018 5:49 am

Isn't activated carbon just crushed charcoal?

You could rig up a small portable filter with nothing but a discarded soda bottle, a couple small BBQ briquettes, sand and gravel. You'd still need to boil it to kill off the microbes that still pass through. I think the bigger designs are better, because the more sand, gravel and carbon they pass through, the purer the end product.

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Re: Off-grid water filtration

Post by SavingWithBabies » Wed Jul 18, 2018 10:16 am

Reverse osmosis is also used in at least a couple of other contexts:
* marine reef tank enthusiasts (and breeders of some freshwater fish)
* home water filtration (sometimes just drinking, sometimes brewers)

A good home unit for say the marine reef enthusiast can cost around $400-500. This is expensive but quite a bit less than the units used on boats. The boat units need a high pressure pump that consumes not too much energy (think boat, solar, batteries -- not wanting to run generator). The home units can get by without it however you can increase your yield of filtered water with one. But a home pressure pump can cost around $150 as we have easy access to power and there must be other reasons I don't quite understand for the price difference.

If you're not familiar with reverse osmosis, the yield mention above should draw your attention. How it works is water comes in and is usually filtered by a bunch of canisters for particles. Then it comes to a reverse osmosis filter and that lets pure water through and the containments are increased in the another output which is waste water. So you'll have water come in and then exit in two stream: good pure water and waste water. If your pipe water pressure is low, you can use the electric pressure pump mentioned above to raise the pressure which increases the yield of good water.

I've read the waste water is a tricky thing. It's tempting to use that to water your garden but it has increased everything so it may be bad for your soil. I personally sent it right back down the drain which seemed quite wasteful (however I was on a second floor apartment). I'm curious if anyone knows more about uses for the waste water. If I was doing this today, I'd be tempted to try to mix it with rain water and then use that to water the garden.

My strategy is to live close to these:


(but filtration would still be required)

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