Water contains non-essential dissolved minerals. These can be present in bicarbonate, sulfide and/or oxide form. The most common of these is chloride which makes up about 85% of all dissolved mineral content. Other widely occurring anions include fluoride, phosphate, silicate, nitrate and carbonate.
The average total concentration of these solids is 30 grams per liter (a little over 8 oz. per gallon). Total dissolved solids or TDS are sometimes expressed as milligrams per liter (mg/l) but this practice has become less popular recently due to possible confusion with parts per million measurement for pollutants in water. A more accurate measurement unit is electrical conductivity expressed in micro-Siemens or µS/cm.
If you have ever tasted mineral water, you will have noticed the distinctive taste caused by dissolved minerals. Bottled mineral water is usually taken from natural springs which are fed by groundwater flowing through rocks containing soluble minerals. Distilled water contains practically no solids at all so it tastes salty because of the sodium chloride content of normal sea salt. The oceans are also salty because they contain many soluble salts derived from rocks worn away by rivers and glaciers over millions of years.
- Distillation also called vapor distilled water is an excellent purification technique for seawater because salts concentrate in the boiling brine leaving nearly pure water behind as vapor condenses to form freshwater (distilled) drinking water. This process makes the water very pure but also leaves all the non-soluble mineral salts behind so it is slightly acidic.
It was once common to add minerals back into distilled water to make it less corrosive (and therefore pump able) and less likely to leave deposits of scale on hot metal surfaces like kettles or inside kettles. These days, most people prefer that their water has no taste at all which means they will use a filter instead that removes many of these natural solids.
Chemical purification can be used if there are particular soluble ions in the water like chloride, sulfate or nitrate which make it undesirable for some reason. Adding chemicals like ozone or chlorine can remove these impurities but process does not remove any particulate material so it may require further filtration. Very small quantities of chlorine can be removed by boiling the water because this drives off much of the oxygen dissolved in the water as well.
- If you are drinking vapor distilled water straight from a still, then it is usually recommended that you take an ion supplement to replace any essential salts that have been washed out. The reason being that your body needs these salts for proper muscle and cellular function.
It seems wasteful however to distill relatively pure tap water just to strip it again of all minerals when the resultant drinking water contains next-to-nothing anyway! Distillation is not really necessary if using other types of filtration. All other types (including activated carbon) remove many soluble solids like metals and pesticides that distillation does not take out.
Distilling any liquid will remove the volatile organic compounds (VOCs) like alcohol and benzene which pass easily into steam but this is not harmful unless you drink them! Water, for example, contains negligible amounts of alcohol or benzene even in quite polluted areas. Distilled water does however contain no VOC’s whatsoever so it is great for using in solar stills to make seawater safe to drink.
Although distilled water tastes ‘flat’ and looks clear like pure water should, it can be difficult to find where to buy high quality distillers these days.
- The only way left then may be to get a household still and make your own distilled water from tap water! This is not as difficult as it sounds but you do need to be aware of a few important details.
You can make distilled water by boiling and evaporating seawater (seawater desalination) or brackish well or river water (brackish groundwater desalination). The distillation process for both is the same except that seawater must first be boiled and recon distilling to make it less acidic and corrosive. It takes about three liters of tap water to produce one liter of distilled water.
- Distillation does nothing more than purify your water so it is best used on relatively clean supplies rather than filthy ones.