Improvise a distillation setup

Every other method on this site separates things out of water. Distillation does the opposite: it takes the water out of the things. That single difference is why it succeeds where everything else fails, and why it costs so much fuel.

You will probably never need it. When you do need it, nothing else will do.

When distillation is the only answer

That table is the whole case for knowing this. Four of those six rows are situations where a household would otherwise have no option at all, and one of them (algal toxins) is a case where the instinctive answer actively makes things worse.

The realistic British scenarios: a coastal household with the mains down and only sea water available; a private supply contaminated by something chemical; road-salted snow as the only water in a hard winter; a nitrate-loaded borehole.

The fuel problem

Be clear-eyed about this before building anything.

Heating a litre of water from cold to boiling takes about 419 kJ. Evaporating that same litre, once it is already at boiling, takes about 2,257 kJ, because breaking water out of the liquid into vapour costs far more than merely warming it.

So evaporation is roughly five and a half times the energy of getting it to the boil in the first place, and a distilled litre costs something like six and a half times a boiled one before any losses. On a wood fire, at realistic efficiency, you are looking at a serious armful of dry wood per litre of distilled water.

The consequences:

• Distillation is not a water supply. It is an emergency measure for the specific problems above.
• Always distil the smallest volume that solves your problem. Distil drinking water only. Wash, flush and clean with the untreated water.
• Recover the heat if you can. A distillation rig sitting on a stove you are already running for heat or cooking is nearly free. The same rig on a dedicated fire is expensive.
• If the problem is only microbes, do not distil. Boil, which costs a sixth as much fuel. Distillation is for what boiling cannot fix.

The pot-and-lid method

The simplest rig, buildable from an ordinary kitchen in ten minutes. Low yield, but it works and it needs nothing you do not have.

What you need: a large pot with a domed or dished lid, a smaller heatproof container that fits inside, and a heat source.

1. Put the contaminated water in the big pot, a few centimetres deep. Not too much, because the collector must sit clear of it.
2. Stand the small collector container in the middle, on a trivet, a stone or an upturned saucer so its rim is well above the water level.
3. Invert the lid so it dips down into the pot, its lowest point directly above the collector.
4. Heat gently. You want a steady simmer, not a rolling boil. A violent boil splashes contaminated water into the collector and ruins the whole batch.
5. Put cold water, or snow or ice, on top of the inverted lid. This is what makes the method work: the temperature difference is what condenses the steam. Refresh it as it warms.
6. Steam rises, hits the cold lid, condenses on the underside, runs down to the low point and drips into the collector.

Yield is modest, perhaps a few hundred millilitres an hour on a good rig.

The tube condenser, which is far better

If you have any pipe or tubing, build this instead. Yield is several times higher and the condensate never comes near the source water.

What you need: a pot or kettle with a lid you can seal reasonably well, a length of tube (copper pipe, food-grade silicone, or a metal kettle spout extension), a container of cold water, and a collection vessel.

1. Seal the tube into the pot lid or the kettle spout. A kettle is close to ideal because the spout is already there. Seal joints with a flour-and-water paste, clay, or wet cloth, which is entirely adequate at these temperatures.
2. Run the tube downhill, away from the heat, through a container of cold water. Coiling it in a bucket of cold water is the classic arrangement and works extremely well.
3. Deliver the tube end into your clean collection vessel, which sits well below and well away from the fire.
4. Heat to a steady simmer. Steam travels along the tube, cools in the coil, condenses to liquid and runs out the far end.
5. Keep the cooling water cold. Refresh it or run a trickle through. Once the cooling bath is hot, the whole thing stops working, and this is the usual reason a rig that started well tails off.

Materials to use and avoid:

• Copper pipe is ideal. Standard 15 mm plumbing pipe, clean, unsoldered where possible.
• Food-grade silicone or PTFE tube is fine and easy to coil.
• Never use lead solder joints, garden hose, or any plastic not rated for boiling. Hot steam pulls plasticisers and stabilisers out of unsuitable plastic, and you would be adding contamination to water you are distilling precisely to remove it. This is a genuine and commonly-made error.
• Never use galvanised pipe or fittings. Hot steam and zinc coating do not mix.

Discard the first small amount that comes through. It carries whatever was in the tube, and if the source is chemically contaminated it may also carry the lightest, most volatile fraction. Throw away the first 50 to 100 ml.

What distillation does not fix

The practical rule: distillation is for what does not evaporate (salt, metals, minerals, nitrates, toxins, every organism) and useless or harmful for what does (fuels and solvents). Use your nose. A chemical or fuel smell means walk away, not build a still.

Running the vapour through activated charcoal afterwards helps with some volatiles, but that is a reduction in risk rather than a guarantee, and it is not something to bet a household on.

Drinking distilled water

Distilled water is very pure, which brings two minor issues worth knowing about and neither is a reason to avoid it.

It tastes flat and unpleasant. The taste of water is mostly dissolved minerals, and distillation removes all of them. Pouring it back and forth between two containers a few times aerates it and improves the taste considerably. A very small pinch of salt per litre helps too, which also addresses the second point.

It contains no minerals or electrolytes. For a few days this is of no consequence. Over weeks, as the only water source, alongside a restricted diet and any fluid loss from heat or illness, it contributes to electrolyte depletion. Eat normally salted food, and if anyone is unwell with vomiting or diarrhoea use oral rehydration salts at the ratio on the medical page rather than plain distilled water.

Neither of these is remotely as important as the contamination you removed. Distil first, worry about minerals later.