Acidity of Water – How to Measure It

Water is a chemical compound with two hydrogen atoms and one oxygen atom. The chemical formula for water is H2O. Carbonic acid is produced when water is dissolved in carbon dioxide, which raises the acidity of water or the liquid in the subject. The higher the acidity, the more carbon dioxide has been dissolved in water.

Seawater has higher acidity than freshwater because it contains more dissolved carbon dioxide. Freshwater has a pH of 6 to 7, while seawater has a pH of about 8.

What is Acidity?

Acidity is a measure of an aggregate property of water that can only be interpreted in terms of specific substances if the sample’s chemical composition is known. According to the method of determination, strong mineral acids, weak acids such as carbonic and acetic, and hydrolyzing salts such as iron or aluminum sulfate may all contribute to the measured acidity.

How to Measure Acidity?

Acidic waters are corrosive, so measuring acidity is critical. Hydrogen ions present in water samples as a result of solute dissociation or hydrolysis react with standard alkali additions.

Learn: How to Measure Alkalinity of Water

Thus, acidity is determined by the end-point pH or indicator used. The construction of a titration curve by recording sample pH after successive small measured additions of titrant allows for the identification of inflection points and, if present, buffering capacity, as well as the determination of acidity with respect to any pH of interest.

Causes of Acidity?

Dissolved CO2 usually is the major acidic component of unpolluted surface waters, handle samples from such sources carefully to minimize the loss of dissolved gases. In a sample containing only carbon dioxide bicarbonates carbonates, titration to pH 8.3 at 25°C corresponds to stoichiometric neutralization of carbonic acid to bicarbonate.

Related Study: Determination of Biochemical Oxygen Demand

Because the color change of the phenolphthalein indicator is close to pH 8.3. This value is generally is accepted as a standard endpoint for titration of total acidity, including CO2 and most weak of the acids.

pH Level of Water

So a water’s acidity is its quantitative capacity to react with a strong base to a specific pH. The measured value can vary greatly depending on the end-point pH used. In terms of determination.

Acids contribute to corrosivity and have an impact on chemical reaction rates, chemical speciation, and biological processes. The measurement also reflects a change in the source water’s quality.


1.    Take 100 ml of the water sample into a conical flask Add 1 drop of N/10 sodium thiosulfate solution to destroy any residual chlorine.

2.    Add 2-3 drops of methyl orange indicator and titrate against N/50 NaOH solution until the red color changes to yellow. Note down the titer value.

3. In Another flask take a 100 ml fresh sample and add 2-3 drops of phenolphthalein indicator and titrate against N/50 NaOH. Until the solution is turned to pink color and the color persists for at least 20 seconds. Record the NaOH used.

4.    Calculate the acidity as follows:

For methyl orange endpoint (pH 3.2 to 4.4)

Acidity =(Titre value X acidity factor)/volume of the sample in ml.

Acidity Factor: 0.025 N/50 NaOH=0.0001N

For phenolphthalein end point (pH 8.3)

Acidity=(Titre value X acidity factor)/volume of the sample in ml.

Acidity Factor: 0.025N/50NaOH=0,0001N

Acidity of Water

Best pH of Drinking Water

Drinking water should have a ph level between 6 and 8.5, with 7 being neutral. Anything below that is considered acidic, while anything above that is considered basic.

Also read: Turbidity Lab Report using Advanced Turbidity Meter

An ideal ph level for drinking water allows the water to be easily absorbed by the body and aids in the maintenance of a healthy mineral balance in the body. Extremely acidic or basic water can be harmful to one’s health, causing digestive issues and increasing mineral loss.

Test pH of Water

There are several methods for testing ph levels in drinking water, including chemical tests with ph strips or tablets and more advanced methods like titration and spectrophotometry. The best way to ensure that your drinking water has an appropriate ph level is to test it at home using one of these methods on a regular basis. If the ph level of your solution is found to be outside of the recommended range, you may need to adjust the ph level of your solution.

Why is the acidity of water important?

1. Water treatment is disrupted by acidity, which makes it difficult or impossible to treat water.

2. It corrodes pipes.

3. Aquatic life will be affected by abnormal acidity levels.

4. The pH(Acidity) of this water is 6.5, which is slightly more than neutral and just a little less than ideal. From the public health viewpoint, the presence of acidity due to free CO2 has no significance. Mineral acidity (H2SO4, HO, and HNO3) in water is nevertheless unacceptable.

5. Water with a pH greater than 50 mg/L is not suitable for R.C.C. works and plants.

Chemistry of Indicators

Indicators are chemicals that change color when the pH of the solution is changed. Indicators are absorbed on the paper during pH paper’s operation. The changes in acid-base indicators are based on pKin values.

Chemistry of Indicators
Chemistry of Indicators


To summarise, it is critical to be aware of the acidity levels in water and to take precautions to ensure that you are drinking water with a pH level that is beneficial to your health. We can help reduce the risk of developing diseases and maintain good overall health by keeping our bodies hydrated with clean and healthy water. What tips do you have for making sure you drink enough clean, healthy water every day?

Acidity is an important aspect of water that should be considered when looking for the best drinking water. It is important to have a pH level that is healthy for the body and helps to reduce acidity levels. We hope this article has helped you understand more about what acidity is, how to measure it, and why it matters.

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