The purity level distilled water (DW) is much more than what we normally call pure and deionized water. There are many uses of DW in research studies, scientific laboratories, and hospital applications, where sterilized type of water is required. The pH level has something to do with the distillation process of water.
What is Distilled Water?
Water purified with distillation method results in distilled water. The purification system, in which water is boiled first to form steam in an enclosed apparatus is called 'still'. The steam is condensed in a sterilized container called condenser. Thus, in the boiling step, all microbes are killed and impurities are left behind, while only the steam part is collected in the condenser. Whichever the source of water (river, lake, ocean, etc.), the purity of distilled water is found to be more than 99 percent.
Information on The pH Level
Most people assume that the pH of DW is neutral or near neutral. With respect to the preparation procedure, and expelling of gases during boiling, it is understandable that the pH scale falls in the neutral range (pH 7). Nevertheless, in most cases, it is slightly acidic (around pH 5.8). Some sources report that the pH level to be as low as 5.5. Generally speaking, the pH of distilled water is below 7 or neutral value.
Practically, it is very difficult to get distilled water with neutral pH in regular equipment setups. The slight acidity is because of the carbon dioxide (from air) that gets dissolved in the water during condensation, forming carbonic acid. At low temperature, dissolution of CO2 takes place, till it achieves a dynamic equilibrium with that of the atmosphere. To be more precise, the amount of carbon dioxide absorbed during condensation equals the amount expelled during boiling. Ultimately, the carbonic acid increases acidity of distilled water, and lowers the pH level to below neutral value.
pH Value of Double Distilled Water
Double Distilled Water, referred to as ddH2O in abbreviation, is used when there is a need for increased purity level, more than that of the normal water prepared by single distillation process. As the name suggests, water is subjected to repeated distillation (for two times) in order to produce ddH2O. It is basically used for molecular biology experiments that require optimal sterility. Similar to single distilled water, the pH level of double distilled water is slightly acidic (below pH 7).
For bringing the pH to a neutral value, a gallon of distilled water requires ⅛ teaspoon of baking soda. It is not unusual to use DW for drinking purposes. Some households use the process of distillation for water purification, especially in areas where tap or municipal water is not safe for drinking. Considering the fact that DW is free of dissolved minerals, ions, and gases, it tastes bland.