Last modified on 22 September 2009, at 12:44

When It Hits the Fan/Water Desalination

(The following comes from a post and comments at http://dailypundit.com/?p=35912. Used by permission of the site owner. Will upload images after I get explicit permission from the owner; for now you can see them at the original site. I intend to completely rewrite the page in more expository form, but this will do until I have time for that.)

I have an unlimited water supply within a couple blocks of my house called the San Francisco Bay. The only problem is that the water is brackish to seawater salty. Undrinkable as is, in other words.

So I’ve been grappling with the problem of desalination for some time. I first tried a home osmosis filter, but it wasn’t powerful enough to handle salt water. Next I looked at “solar distillers,” which are basically large, unwieldy boxes set up to distill water by the power of the sun - like this one:

TODO: image 1

(Check out the ripoff - $245 for plans and a few cheapo fittings so you can “build your own.” Otherwise, almost $500 for the manufactured version.

So I looked at so-called “campfire stills” - stainless steel stills designed to distill water with nothing but a heat source. Here’s an example:

TODO: image 2

This one costs $380 U.S. plus shipping.

Here’s another one, not quite as expensive:

TODO: image 3

But pricey enough, only ten bucks cheaper.

All of this struck me as ridiculous. The principles of design seemed simple enough: You needed a reservoir of boiling water, and some way to condense the steam and catch the distilled runoff from the condenser.

This is what I finally came up with:

TODO: image 4

The parts consist of one stainless steel pot lid ($1.79 at Goodwill), one stainless steel 1 gal bowl with small side handles ($.79 at Goodwill), two hook bolts and matching nuts ($.87 at Ace Hardware) and one stainless steel stock pot, 11″w x 10″h, $33.00. Total cost: $36.45.

I’m still tinkering, but it is generating about eight ounces of distilled water per hour, or a gallon in 16 hours.

This is terribly inefficient - the professional stainless steel jobbies claim as much as 100 ounces per 1.2 hours.

I have some ideas, though. I think the condenser needs to work better. Probably it needs cool water in the lid to maximize condensation. In order for that to work properly, I’m going to have to get some rubber washers to seal the holes where the hook bolts are connected:

TODO: image 5

I think I’ll also try a different inverted lid, to see if I can make the drip of the condensed distilled water into the catch bowl a bit more efficient as well.

This is a proof of concept deal. Once I get it working at its most efficient, I’ll post some more photos of every aspect of it, along with final production figures.

Any suggestions for improvements will be highly appreciated.

One note: Even at their most efficient, the stainless steel pro versions are inefficient in relation to the amount of fuel required - an hour and a half’s worth of propane for one gallon of water will exhaust propane fairly quickly. However, I do have some ideas to handle that problem cheaply, too. I just bought a 54″ linear Fresnel lens off eBay for $61. If I’m right, that will give me plenty of water-boiling power, even in San Francisco.

UPDATE: Okay, after changing out the upper lid for one with a better curve, and then adding cool water to the lid every ten minutes, I produced about 1.1 quarts of distilled water in an hour of boiling. Although it would mean a fair amount of work and watching, I could produce a gallon of distilled water in just under 4 hours. That’s acceptable, if not optimal. I’m going to continue to tinker. Maybe if I make the water reservoir on the top part larger - maybe glue a similar size container to the lid or something, but much taller….

How does the water taste? Not bad. It has a very faint tinge of salt. However, the solution I used was one pound of salt to one gallon of water. That’s about 4 times as strong as ordinary sea water, and probably even stronger than that compared to brackish Bay water. It was still definitely drinkable, though.

I’ll try it with the proper ratio of salt to water later, or maybe even genuine Bay water - and let you know the result. In the meantime, here are photos of all the parts, and how they fit together:

Here’s the collection pot. It’s original, nothing changed. The little wire handles on each side are used to hange it from the condenser lid.

TODO: image 6

And here is the collection pot hanging from the condenser lid. The lid is set on top of the boiling vessel, and cool water is added to the lid to aid condensation. That’s it.

TODO: image 7

I think the the biggest challenge will be to make the condensation process more efficient. Still, my under-$37 water distiller can produce a liter-plus of distilled water from salt water in an hour, and that’s a much better dollar/production ration than any of the big boys can offer. For now, it’ll do.

UPDATE: I’m actually kinda proud of this distiller thing. I’ve been wrestling with the problem for quite a while, and I haven’t seen anything across the entire innertubes that offers such a cheap solution, not even close.

Reader Comments and ResponsesEdit

Comment 1:

If I’m looking at your pic correctly, it would appear you are losing most of the steam and capturing only what condenses on the surface of the upper pot. I think your production would be much greater if you have a pathway for the steam to condense, think chemistry lab or one of those forbidden stills from the hills west of me.

Response:

You’re thinking stainless steel pipe coils, and those are pricey, hard to work with, and hard to find. (You can’t use copper, which is cheaper, easier to work with, and easier to find, because distilled water leaches copper - a lot of copper).

The efficiency of this thing is actually pretty good, as such things go - at least in terms of water conversion. I started with two gallons of salty water, produce overall about .6 gallons of water over the afternoon of messing around with different lids, etc., and had a gallon of very salty water left in the boiling reservoir when I finished up. I think I’d have lost more water if I’d had the heat up higher, but I kept it at a mildly bubbling simmer. I’m going to try it with the heat cranked up to see if I get any more condensate than at lower temps, or if the steam loss results in an unacceptable tradeoff.

Comment 2:

Actually, I was thinking glass or copper. They use copper in stills. ‘Course, stainless will work, and not so expensive if you can bend the stainless yourself. I’ll check into the copper leaching problem.

Comment 3:

Yep, looks like you would want to stay away from copper.

Response 3:

I was operating off this advice:

Non-Electric Distiller by rudenski

   Special Note: The Life Saver Distiller uses Food Grade 316 Stainless Steel in the Condensing Coil to prevent the leaching of hazardous metals into the Distilled Water which will occur if the Condensing Coil is made of Copper or Aluminum.
   Moon-Shiner Expertise incorrectly assumes that since soft copper tubing works just fine for a Condensing Coil in making Bootleg Whiskey, copper can likewise be used in a Water Distiller – when, in fact, Copper is unsafe in making Distilled Water!
   Copper is OK in a Whiskey Still because alcohol does not leach cooper into the Final Product.
   However, this is not the case with the Universal Solvent — Distilled Water – which will leach copper and aluminum out of a coil made with such metals. Thus, the need for Food Grade 316 Stainless Steel in the Condensing Coil of a Steam Water Distiller. 

If somebody can find me authoritative disproof of this notion, I’d be quite happy. As I say, copper tubing already partly coiled is readily and cheaply available at an Ace Hardware less than a mile from my house. And I already have a 12 quart pressure cooker. I believe you can also use plastic tubing as your connectors.

Comment 4:

You need to look into an old fashioned pressure canner with a top vent that can be converted easily into a coupling for your steel tubing. I still think copper tubing is fine for such a still. The trade off is rapid heat exchange in a regular cool water bath.

There are a lot of pluses for a pressure canner/cooker distillation. Increase in efficiency and yield. Anyone who home distills alcohol knows that you want to use gentle heat to release the vapors into the coil system. That same amount of heat combined with the closed system will yield good quality distilled water with minimum loss.

Depending on your needs, you’ll have to pay dearly for a high capacity pressure canner, BUT you get efficiency and yield in return. The closed system is the way to go.

Stovetop stills like this are very common in my area, usually used by people to distill small amounts of alcohol for whatever reasons they have to do so.

Not that I would know anything about that, mind you.

Comment 5:

Here’s a nice little essay on pressure canner water distillation. As the gentleman mentions, this method has multiple uses with the proper understanding. For a long term emergencies, this could allow you to produce medical alcohol for sterilization purposes through a double distillation method.

Not that I’m advocating something like that in frickin’ California, mind you.

Another word about copper. Copper has the advantage of being relatively easy to work with. Stainless steel tubing is a bitch to work with. ‘Shiners have been using copper for ages. Pot stills are copper. I really don’t think its a deal breaker to use copper tubing for your condensation coil, since we can assume that you’re not planning to distill your drinking water for the rest of your life, but only for the duration of the the emergency. For this reason, I wouldn’t be worrying about the amount of copper in your water. It’s going to be negligible in the short term, and not too worrisome in the long term, given the alternative in world outside.

Comment 6:

Why not make it real simple. Stick a Carboy in a tub of brackish water. Put a CPVC pipe into the carboy with a couple inches of water. Hook up the steam source to the other end of the CPVC pipe, and bubble the steam throught the water in the carboy.

Comment 7:

It’s difficult to find an exact proof, but as I said above after checking a few chemistry points, probably not a good idea. It would appear hard water is good for copper, as far as leaching goes and distilled water not so much because of the ph. I also made the assumption that it was OK since it is commonly used in shine making. Of course, they’ve also been known to use a lead based car radiator or two, leading to a painful death from lead poisining. I’d stay away.

Comment 8:

Look up “solar still” a hole in the ground with a recpticle for catching water and a sheet of plastic spread over the hole with a weight in the center over the recepticle to form a cone. You pour untreated water in the hole, set the recepticle and plastic sheet in pleace and let the sun do the work. Very inexpensive: http://en.wikipedia.org/wiki/Solar_still

Response 8:

That was the very first thing I saw when I originally began researching this. Unfortunately, it isn’t very practical for a condo located in a San Francisco ghetto.