pH is an abbreviation or symbol which stands for Potential of Hydrogen. The pH scale is a manner of describing the level of acidity or alkalinity solution in water. The basic formula of pH is pH = log10(1/[H+])= -log10[H+] and the H+ of the formula represents the hydrogen ion in the solution. The pH has three basic stages. Each stage of pH depend on the amount of acid or alkali that is included in the solution. The stages are starts at the point 7 which is well known as freshly distilled water (pure solution without acid or alkali). And when the solution contains more acid than freshly distilled water, the number of pH stage decreases, and when the solution contatins more alkali than freshly distilled water the number of pH stage increases. 
Three stages of pH
pH scale : less than 7
The acidic solution contains more acid than freshly distilled water. Its stage number is less than point 7; the freshly distilled water, and it contains less hydrogen ions than the other two stages.
There are some examples of acid solution
1) Orange juice : pH scale 3.6
2) vinegar : pH scale 3
3) Coffee : pH scale 4.9
pH scale : center point 7
The neutral solution has no positive or negative charges, the most well knwon neutral solution is freshly distilled water.
There is only one example of neutral solution
1) Freshly distilled water
pH scale : greater than 7
The basic solution contains more alkali than freshly distilled water. Its stage number is higher than point 7. And it contains more hydrogen ion (H+) than the other two stages.
Some examples of basic solution.
1) Blood : pH scale 7.4
2) seawater : pH scale 8
3) baking sode : pH scale 9.2
The most well known way to determine the pH of a substance is by using ‘Litmus paper’. The Litmus paper was made by Arnaldus de Villa Nova the Spanish alchemist. There are two types of Litmus paper; red and blue. The red paper is used to define the basic solution, and when it is put into a basic solution, the color of paper changes to blue. On the other hand, when the blue paper is put into an acidic solution, the color of paper changes to red.
Alkali water drink
Nowadays, there are many various type of alkali water. It is often used for sport drink; thirst stopper. And it is actually used by many athletic players. But here is a question, why is it alkali water? Why is it not like fresh water the neutral water? And here are some reasons why we should drink alkali water instead of neutral water.
1) pH scale of ph is 7.35 ~ 7.45, higher than the neutral solution which is the basic solution. And since the blood is basic solution, alkali water which is basic solution fits well to human body.
2) Usually normal adult’s body is 70percent water. And something that has higher or less than pH scale range 7.35~7.45 can hurt human body. So it is good to drink the alkali water which has basic solution like our human bodies.