pH of Water Summary
The term pH refers to a scale by which to measure how acidic or basic (alkaline) a substance is.
Acidic substances have a sour taste, and basic substances have a bitter taste.
When it comes to water, there are many factors which can contribute to the acidity or basicness of water.
In other words, not all acidic water is the same, not all basic water is the same.
Our bodies, in particular our blood, is in the range of 7.34-7.45 on the scale. This is in the neutral pH, to slightly basic range. (1)
To form an objective opinion or make an objective decision about the water you drink, you need to know and differentiate between the factors that are contributing to the acidity, neutrality, and alkalinity/basicness of the water.
Read on below to learn about these contributing factors or jump to our What is Alkalinity page which goes in depth on contributing factors.
What is pH & How does it relate to Water?
Acidity vs alkalinity of a substance is measured on the pH scale which is a scale from 0 to 14.
This scale is a base 10 logarithmic scale which is similar to how the strength of earthquakes are measured.
What this base 10 logarithmic scale means is that every single digit move on the scale indicates a factor of 10.
So that means a two digit move on the scale indicates a factor of 100, 10 x 10 = 100. As a further example 3 is 10 times 2, 4 is 100 times 2; and 5 is 1000 times 2.
Learn more on how the logarithmic scale works on Wikipedia’s explanation page here.
The Math Behind the pH of Water
Digging into the math of this pH rating scale, it’s interesting to distinguish that pH is measured on a logarithmic scale.
This means that the higher the concentration of H+ ions, the lower the pH or in other words the more acidic the substance.
Example of pH Calculated
Let’s consider the formula calculating the pH of pure water:
pH = – log [concentration of H+] = – log [1 x 10-7] = -[-7] = 7
In English the formula above is as follows, the pH equals the negative log formula of “the concentration of H+ ions” (in solution); which for pure water is (1 x 10-7) “Moles of ions” PER Litre.
A mole is a measurement basis for number of atoms, molecules, ions or electrons. It is an SI unit, just like a kilometer, degree Celsius or kilogram. Check out these pages on Wikipedia for in depth explanations on the unit Mole, or Molar concentration:
Wikipedia – Molar Concentration
The base 10 logarithmic formula asks the question, “by what exponent is the number 10 raised to, to equal the number we have inputted into the equation?”
Another helpful page from Wikipedia if you need to brush up on your exponential skills:
Further Example of pH Calculated
For a further example, in water with a molar concentration of 1 x 10-5 H+ ions per litre, there is a greater concentration of H+ than in neutral water (as above), and when put through the pH formula it has a pH of 5 which is acidic.
What is pH Really Measuring
What this scale is actually measuring is the molar concentration of the activity or potential (think of this as the energy) of hydrogen ions within a specific volume. An easy way to remember this is that “pH” is the “potential” of “hydrogen” in a given solution, the energy of the hydrogen in that solution.
The potential of the species in a mixture is dependant on what is referred to as its “activity” in the mixture or its “effective concentration” in the mixture. The more of the species within a mixture of a given volume, the higher its potential will be, the higher its effective concentration will be.
Looking back to our examples, the higher the potential of hydrogen H+ ions in a solution, the higher the concentration of them in solution and the lower or more acidic the pH of that solution.
How Does pH Relate to Water
Regarding water and measuring the potential of hydrogen, or pH, it may sound odd to measure hydrogen. How do you measure how much hydrogen is in water? After all water is composed of H2O molecules, so what are we really measuring?
The key term is the measuring of the concentration of the energy or activity of the hydrogen ion. An ion, in a molecular sense, means a molecule with a net positive or negative charge. Hydrogen ions can therefore be a cation (positive ion) or an anion (negative ion). Also known by their general names, “hydron” for a positive hydrogen ion, and “hydride” for a negative hydrogen ion. (3)
Water in its pure form, H2O, will actually disassociate itself in the following formula:
H2O ⇌ H+ + OH−
The H+ from the formula above is the acidic causing hydrogen ion which we are referring to. Water will naturally disassociate itself per the above formula, and depending on minerals in the water may break itself up and bond with them as well.
Certain alkaline substances, carbonate minerals for instance, can dissolve in water and create a reaction resulting in many negative ions which will raise the alkalinity of the water. Alkaline substances in particular carbonates are what causes the water found in nature to be so alkaline.
Acidic water can be caused for many reasons, pollutants, acids, heavy metals, additives to city water for disinfection, can all cause water to become acidic when they come into contact with each other.
The most common cause of acidic water is simple carbon dioxide found in the air. When the carbon dioxide in the air comes into contact with water it will react to form something called carbonic acid. The carbonic acid molecule, H2CO3, has a readily available H+ ion to give away which leads to the overall acidification of the water.