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:
(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:
This one costs $380 U.S. plus shipping.
Here’s another one, not quite as expensive:
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:
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:
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.
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.
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.
Next up: modifying a 5 cubic foot freezer to act as a refrigerator that cools contents to 36-38 degrees using only about three hundred watts per day – an amount easily manageable by a solar panel of less than a hundred watts.
Refrigeration would be a huge boon in any extended power outage. Otherwise, you have to eat everything you cook when you cook it.
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.