All pH charts have different scales of colors representing the various levels of acidity, neutrality or alkalinity. Although the colors can vary from chart to chart, it is commonplace that pH zero (highest acidity) is represented by the color red. Examples of substances that are between pH zero and 4, regarded as strong acids, are battery acid, lemon juice, vinegar and acid rain.
The alkaline end of the scale is usually represented by dark blue or purple colors. Typical substances that are described as strong bases show up on the pH scale between pH 10 and 14, and they include substances such as lye, ammonia and milk of magnesia.
The neutrality of pH 7 is often represented by either white or green on the scale. PH 7 is used only for what is regarded as "pure" water, although it is very uncommon to find water that is exactly pH 7. According to United Utilities, the advised level of pH in regular drinking water from household taps should be between pH 6.5 and 9.5.
PH charts are used at every level of science by chemists and biochemists, chemistry and science teachers in schools and swimming pool owners and proprietors. When testing in schools during experiments, it is common that educators will use a pH testing kit or litmus paper, which changes color when exposed to acid or base products. Dipping a piece of litmus paper and having it turn red, for example, would indicate acidity. Swimming pool users are advised to check the pH levels of their pools once each day when they are regularly in use; a safe and comfortable range for swimming pools is between pH 7 and 7.8. Many swimming pool owners achieve this using specialist swimming pool testing kits which show both pH and chlorine or bromine levels.