The pH scale is used to determine whether a substance is acidic or basic, and to calculate how strong a chemical it is. A pH value is a number that ranges from 1 to 14 for most common chemicals, with seven being the middle or neutral point. Values below 7 are indicators of acidity, which increases as the number decreases, while values above 7 indicate alkalinity, which increases as the value increases. One interesting thing to note here is that the pH scale is not a linear scale. In other words, an acid with a ph of 3 is not twice as strong as an acid with a pH of 6. An important distinction to understand is that the pH scale is a logarithmic scale.

On this scale, a substance with a pH of 3 is ten times more acidic than a substance with a pH of 4, and 100 times more acidic than a substance with a pH of 5. Similarly, a substance with a pH of 9 is ten times more alkaline than a substance with a pH of 8, and 1000 times more alkaline than a substance with a pH of 6.

Most natural soft water falls in the range between 5-7, while most natural hard water falls between the range of 7-9

The formal definition of pH reveals that is simply a measure of the activity of hydrogen ions in a given solvent. Activity here means that their movement is free, which is only possible if the chemical has ionized, thus releasing ions into the solution.