Distilled water has a much higher purity level than filtered water and deionized water. Uses of distilled water are many in research studies, scientific laboratories, and hospital applications, where sterilized water is required.
The distilled water pH level has something to do with the distillation process of water. Before discussing about distilled water pH directly, let’s take a look at what distilled water is, and the procedure for preparing it.
What is Distilled Water?
Water purified with a distillation method results in distilled water. By distillation, we mean the water purification system in which water is boiled first to form steam in an enclosed apparatus called ‘still’. Then, the steam is condensed in a sterilized container, called a condenser.
During the boiling step, all microbes are killed and the impurities are left behind, while only the steam is collected in the condenser. Regardless of the source of the water (river, lake, ocean, etc.), the purity of distilled water is found to be more than 99 percent.
Distilled Water pH Level
Most people assume the pH of distilled water to be neutral or near neutral. Thus, ‘is distilled water pH neutral’ has been a common query among science students, who have just started learning chemistry.
With respect to the preparation procedure and expelling of gases during boiling, it is understandable that the distilled water pH scale falls in the neutral range (pH 7). Nevertheless, in most cases, the pH of distilled water is slightly acidic (around pH 5.8). Some sources even report the distilled water pH level to be as low as 5.5. Generally speaking, the pH of distilled water is below 7 or neutral value.
No doubt, the ideal distilled water pH level is 7. But, practically, it is very difficult to get distilled water with neutral pH in regular equipment setups. The slight acidity is due of the carbon dioxide (from air) that gets dissolved in the water during condensation, forming carbonic acid.
At low temperatures, dissolution of carbon dioxide takes place until 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 the acidity of distilled water and lowers the pH level to below neutral value.
Double Distilled Water pH Value
Double Distilled Water, referred to as ddH2O in abbreviation, is used when there is a need for an increased purity level, more than that of the normal distilled water prepared by single distillation of water.
As the name suggests, water is subjected to 2 distillation cycles in order to produce double distilled water. It is generally 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). The reason remains the same, absorption of carbon dioxide by the steam during the condensation step.
So, this was a brief overview concerning distilled water pH level. I hope you have understood the phenomenon behind the acidity of distilled water, despite the sophisticated procedure. For bringing the pH to neutral value, a gallon of distilled water requires 1/8 teaspoon of baking soda. It is not unusual to use distilled water for drinking purposes. Some households use the process of distillation for purifying water, especially in areas where tap water or municipal water is not safe for drinking. Considering the fact that distilled water is free of dissolved minerals, ions and gases, it tastes bland.