Fractional distillation – the process


I don’t know about you but when I first heard of drinking distilled water a few years ago, it immediately reminded me of those squirty bottles of distilled water we were provided with in our school days in science lessons. Was that the same for you, perhaps? I also got to play with these squirty bottles well into my early 20s as I chose to do my degree in Chemistry and we had 2 lab days a week. During that time, I did dozens upon dozens of fractional distillation procedures, and they were actually always my favourite. I just loved the flasks and conical gear and setting it up from my personal stash of glassware, the shapely bottles, the skill of being able to produce a pure substance at the end of it (if you were good enough), waiting for just the right time to collect your pure sample; any sooner or later and you would have a contaminated sample; then heading over to the spectrometer to confirm the makeup of your substance. It really was my favourite type of procedure. I still do it to some extent as demonstrations for my school kids, but it’s less often now. Here’s a video to remind you of what it is.

So, fractional distillation is a separation technique. When you have a liquid and solid mixed together, you can easily use a barrier filtration system to separate the two substances. When you have a solid dissolved in a liquid, you can use evaporation to isolate the desired solid. But when you have 2 or more liquids mixed together, including solutions (which are solids dissolved in a liquids), how on earth would you separate them? fractional distillation lab apparatusWell, we utilize the fact that all liquids have different boiling points. And in a lab, you simply start heating up a mixture and hold a thermometer over it, measuring the temperature of the fractional distillationgases being released. You would already know the boiling point of your desired product, and so you know that anything else that boils at a different temperature would be a different substance. So, as you noticed the temperature slowly rising and you saw some gas product coming off you would know that that was not your desired product and you would let all the gas product escape. Or if you were condensing it, you would collect it in a separate container and discard of it. Then as soon as you hit the correct temperature, you would change the collecting flask and let the apparatus condense the gas. If you kept the heat on to increase the temperature, you would then be collecting some other by-product you didn’t want and you would change the collecting flask so that there was no contamination of your desired product. The end result would be a conical flask full of only your desired product, and no other type of molecule at all. This is called a pure substance, when you have collected only one type of molecule. I hope I have explained this well. (By the way, there is no other way we use to separate and purify a substance of mixed liquids that doesn’t involve chemical reactions, there is only fractional distillation. It is this process that is used to separate all the different products we get from oil. You can find simple school version descriptions of it).

I don’t know if you find this interesting, but I love it. it’s just so simple.

In a similar way, can you now see how your water distiller works? In a well-made distiller, the lower boiling temperature substances would boil off first and escape through a vent, these are often called VOC’s. The pure water would boil at 100 degrees Celsius and be cooled down for collection. A good distiller will cut off at 100 degrees. Any substances that boil at higher temperatures would not boil off at 100 degrees and so would stay in the unit. Ideally, you would not want to be doing any condensing until you hit 100 degrees, as you will only be collecting undesirable stuff. Most distillers don’t work like this, they have a continuous fan. So, many people have a good result by throwing away the first 20 mins worth of liquid that comes out of a distiller, as it may contain some VOC’s. This is also why the carbon filter is used.

The only way to get around this is to 1) throw away the first few mins of liquid as already suggested, and/or 2) filter the water before you use the distiller, by using another carbon water filter; just use one of those Brita water filters to filter your tap water before you then distil it, click here to see one, or 3) get a very expensive auto-fill large water distiller that range from $1500 to $4000, ouch!!!

Me, personally, the water is pure enough for me when I do steps 1 and 2. And that’s what I do. I have a XL Brita water filter, 2-3.4L, so my distiller just takes two full jugs from my Brita filter.

(Now that I’m thinking about it, I guess if you really wanted to go even extra, you could also/or boil the water in your kettle before putting it in your distiller. (My kettle is glass, has a hidden element which is ideal, and the internal base is stainless steal) I’ve even heard of some people who choose to use reverse osmosis on their tap water first, then they filter it using a Brita jug, then they use a countertop water distiller. And they do this everyday).

Honestly, if I could easily afford it, why wouldn’t I go for the more expensive auto-fill types that give me that little extra pureness? But for now, I am very happy with my choice of using a Brita filter and then the countertop water distiller. And by the way, in the absence of a larger auto-fill model this is also the top recommendation of Andrew Norton Webber, well-known and well-versed in the field of distilled water. (More on his recommendations when you subscribe with me).

Hope this all helps to know, especially when you are making a long term investment like buying a water distiller.

Keep well!


In summary, here’s your options:


Brita filter

Countertop water distiller

Auto-fill free standing distiller

Glass kettle to just boil your water

Or you could drink tap water 😉

(I discuss R.O. water and bottled spring water on my page ‘Why Distilled?’)