What does pH measure?

pH measures how acidic/basic water is at any given time. This scale ranges from zero having the most acidity, to fourteen having the most alkalinity. The neutral pH is right in the middle (7) and that is where milk lies on the scale. What determines where a liquid lies on this scale depends on how many free hydrogen or hydroxyl ions are in the water; an abundance of hydroxyl ions meaning the liquid is a base, and likewise, an abundance of hydrogen ions meaning the liquid is acidic. As the pH of water is directly related to the chemicals in it, a change in pH is one indicator that the water is changing chemically. This is why pool owners test their pool water for the pH; so that they can ensure that the chemicals in the water are correctly balanced for safe swimming. Another important thing to note about pH is that the scale is logarithmic in that it increases by powers of 10. So, every time the pH goes up another number, it is ten times as strong as the previous number. This is why it is very crucial for pH to be in a certain range to support life and be safe for humans to swim in.