Purifying Chemically Contaminated Water

[sodak]

We have threads going on about 72 hours, etc., but here is the question. I have several small lakes around me, artificial ones for a golf course. Lots of chemical runoff and goose poop in it.

Boiling will take care of the goose part, but not the chemicals. Will distillation ONLY give you pure water, or do chemicals in the water distill out also? Is this water only good for flushing toilets?

I'm interested in what our biologists/chemists have to say about this.

 

[Iboschi]

Distillation is essentially boiling the water and capturing steam. You will have pure H20 if you capture only the steam. The process isn't simple with large quantities and consumes a lot of energy or heat. If you're careful not to burn the last nasty part and cause the chemicals to go airborne (burn them into the air) you'll just have water. When in a SHTF scenario, I would not use water for anything but drinking, just filter/boil or distill first. Hell, if the three headed geese drink it, it's good enough for me.

 

[mdauben]

Lots of chemical runoff and goose poop in it.

Most reputable water filtration systems for backpacking are effective at removing chemicals from water. There is an absolute limit of contaminants per filter cartidge, though, so severly contaminated water might exhaust the cartridge faily quickly. In a bugged in situation you might be able to jury rig something with the home style water filters, which would last longer.

Will distillation ONLY give you pure water, or do chemicals in the water distill out also?

Distillation will get rid of the heavier chemicals like pesticides and herbicides. Lighter stuff like gasoline or some solvents are likely to follow the water through the process, unless you rig up a more complicated fractional distilation system.

As a general example, when you boil contaminated water in a still, you will get stuff out in the following order:

1. Gasoline & Light Solvents
2. Water
3. Pesticides, herbicides, chlorinated solvents, etc.

So, you would want to discard the first of the distilate, then collect the water, then leave some water in the still so you know the heavier stuff didn't boil off, too. I probably would not want to try it except in a real emergency and as the previous poster said, you are going to go through a lot of fuel doing it. Stockpiling and/or caching extra bottled water might be easier and safer.

I'm interested in what our biologists/chemists have to say about this.

Chemist here and I used to work for a company that made residential and industrial water filters and another that analyzed water samples for contaminants.

 

[The REAL Commander]

Quite right. Anything with a lower boiling point than water will become vapor before the water does. This is known as the "light ends" in distillation, most typically with the distillation of spirits, where Methaol, being lighter than Ethanol, will evaporate first. You want to toss out the "light ends" under all circumstances. There are aslo "heavy ends", and typically in distillation of spirits, heavy ends refer to Propanol, which is heavier and comes out last. When simply distilling water, however, it isn't as cut and dry. Often pollutants will form a solution in the water where the light and heavy ends are not so easily separated. By this, I mean some poisons and contaminants will become vapor at the same temperature as water, and thus condense to form a liquid along with the water when distilled. For these reasons, it it not considered a safe method of purifying chemically contaminated water simply through distillation, as often the process merely converts the water AND contaminants into a gaseous state, then back to liquid state without actually separting the two. It really does depend on what is in the water in the first place. A tight aqueous solution will not want to come apart during distillation, but looser solutions will. Since the possibilities are endless in terms of "whats in the water", always remember to be careful and remember that just because you distill it, it doesn't necessarily mean that it is safe to drink. Unless you have a controlled labratory evironment in which you are able to precicely adjust the temerature of the liquid being distilled, you are ball-parking it (as with a campfire/stove) and the margin of error in such an instance is too great and the risk of being poisoned is very real.

 

[beef]

There's not THAT much activated carbon in each filter cartridge, once its absorbed as much nasty stuff as it can, it will release it back into your water.

I've heard of people adding charcoal to their boiling water to absorb some of the nasties too, but have not tried it myself. Would probably help for nasty tastes, but not for serious chemical contamination.

 

[foxyrick]

Another chemist here (head of chemistry and science in a high school)...

Unless it's a drink or die situation, don't even think about it.

To back up what others have said about distillation; it's great in a lab with a fractionating column, accurate temperature monitoring and chromatography to check your results.

As a simple example of how it can fail though, take alcohol distillation. Alcohol boils at a significantly lower temperature than water, so it 'boils off first'... but it's not that simple. Water and alcohol form an azeotrope - effectively a mixture that boils off together, maintaining a set ratio of alcohol to water in the steam. That's why we can't simply distill spirits to pure alcohol.

Water and alcohol aren't the only mixtures to do this.

Unless you know what's in the water, improvised distillation to purify it cannot be relied on alone.


That said, if it is a drink or die situation, then...

1. Stand the water or filter it to remove gross contaminants.

2. Distill, but raise the temperature slowly and monitor the steam temperature as it enters the condenser carefully with an accurate (mercury in glass or laboratory-grade digital) thermometer. Discard any distillate before the temperature reaches 100 Celsius, and a little after to clear the tubes. If the temperature rises above 100 Celsius, discontinue immediately and discard the remains. Never distill to dryness; always leave some mixture behind with the rubbish in it.

3. If you have the slightest concern that there might still be contaminants (if you don't know what was in the water, you do have!) then slowly carbon filter the distillate once it has cooled. Change the activated carbon frequently - its absorptive capacity is finite.

4. Test it on an annoying neighbour first.



Fractional distillation is a method used to separate liquids with close boiling points. Effectively, a fractionating column helps to consolidate each fraction of the mixture in the distillation process, allowing them to be recognised more clearly by obvious (if still small) temperature changes. A fractionating column is easily improvised by filling a pipe with coarsely broken glass or glass beads. Google 'fractional distillation' for more info on that.

If the water source is so bad that it needs fractional distillation... move, find another one, or buy some big tanks and stockpile you own!

 

[GWashington1732]

If you're desperate enough to drink it, you probably don't have time to purify it. You could probably drink it straight up without too much trouble, see if other mammals are drinking it, if they are, you should be okay with a good boiling to remove all the nasty parasites that could be in it. Unless we're talking about some really crazy contaminants it shouldn't kill you, regular pesticides might give you a stomach ache, too much and your kids might be born with an extra leg or eye but I doubt the amounts in lake water will kill you or do you any major harm. Still there are better sources for water, especially around a lake. Remember, lake water evaporates you can use that to collect what evaporates off that will be safe to drink. Rain and snow are usually safe to drink, unlesss there's some serious environmental crap going down.

 

[sodak]

Great answers, thanks to all! I've got just the neighbor to lend the sample to....