What is Alkalinity?

Sept. 14, 2022
Information about water alkalinity measurements, factors that impact it and its importance.

Alkalinity is a water property that is measured by the number of chemicals present. 

This article discusses important information about water alkalinity, including the factors that affect alkalinity, how alkalinity is measured, and the importance of alkalinity in water. 

What is Alkalinity in Water?

Alkalinity is a measure of water’s ability to resist pH changes that lead to acidity, or to neutralize acids, and maintain a fairly stable pH. This ability is usually referred to as water’s “buffering capacity”. 

The presence of certain chemicals, including hydroxides, carbonates, and bicarbonates, affects water’s alkalinity. In simple terms, water with high alkalinity is less prone to becoming more acidic if it is contaminated with acidic water, such as acid rain. 

How is Alkalinity Measured?

Alkalinity is measured with a process called titration. An acid of known strength, called a titrant, is added to the water. 

The amount of acid used to bring water up to a specific pH level is determined by the alkalinity of the water. Once the water reaches the pH endpoint, it changes color. Alkalinity is measured in the unit milligrams per liter (mg/L) of calcium carbonate (CaCO3). 

Alkaline water has a pH of 8 or higher. The pH scale is used to measure the alkalinity of water. Water with a pH of 8 to 10 is considered mildly alkaline, while water with a pH of 10+ is considered very alkaline. A pH of 7 is neutral, while anything lower than 7 is considered acidic. 

How Alkaline is the Water in the U.S?

The EPA has shared a map highlighting the total alkalinity of surface water bodies in the United States. This map is not exact and it cannot account for the changing properties of all water sources within specific locations, but it is a useful general illustration of surface water alkalinity patterns by region. 

The shading on the map indicates the total alkalinity of surface water samples from the tested streams and lakes in the study. The map is a good example of how much alkalinity varies from one region to the next. There are no obvious patterns in alkalinity across the U.S., but the northeast generally has the least alkaline water. 

Factors that Affect the Alkalinity of Water

There are several factors that affect water’s alkalinity.

Soils & Geology

Local geology and the acidity of soils and rocks have a big influence on the alkalinity of water. 

When water passes through soils and rocks that have a high carbonate mineral concentration, water accumulates carbonates and becomes more alkaline. Sedimentary and limestone rocks also increase water’s alkalinity. 

Certain regions have low-alkalinity soils and rocks, and are less likely to affect water’s pH. For instance, areas with mostly igneous rocks, such as granite, usually have lower-alkalinity water. 

Local geology is the biggest contributor to water alkalinity. In regions where rocks and soils have been disturbed or broken up, such as for mining or urban development, water is especially likely to have a high alkaline content. 

Sewage Outflow

The characteristics of the effluent from wastewater treatment plants affect the alkalinity of natural water bodies, such as streams and lakes. Cleaning agents and food residues contain bicarbonates and carbonates that are washed into surface waters from drains, as well. 

pH Changes

Water pH and alkalinity are closely linked. So, if water’s pH changes, its alkalinity changes, too. 

Factors that are known to alter pH are the concentration of dissolved carbon dioxide in water, the temperature of water, which affects the solubility of CO2, and the level of decomposition and organic decay in a water source, which increases the amount of CO2 in water. 

Other Factors

Other environmental factors, such as acid rain, also affect the alkalinity of surface water. Industrial discharge and incorrect waste disposal may increase or decrease the alkalinity of natural water sources. 

Why is Alkalinity in Water Important?

Alkalinity is important for the health and welfare of ecosystems, marine life, and humans. 

Local Ecosystems

The organisms that live in natural water sources are not adapted to living in rapidly changing water conditions. Before industrialization, aquatic organisms lived in waters that had consistent pH and other parameters. There was no acid rain, no chemical spills, no wastewater effluent, and nothing else that could affect the quality of a water source. 

Nowadays, there are numerous causes of rapid pH change. Aquatic organisms thrive in a pH range of 6.0 to 9.0. When water’s pH changes suddenly, the aquatic organisms may become stressed or diseased, or die. 

Wastewater & Drinking Water Treatment

Alkalinity is also essential for wastewater and drinking water treatment. 

Water treatment generates hydrogen ions, and alkalinity is needed to ensure pH remains in the optimal range. If the alkalinity level in water is too low, excess hydrogen remains, causing the pH to drop and reduce the speed of water treatment. Very low alkalinity may even cause the treatment process to stop altogether. 

Water treatment facilities use soda ash to raise pH and alkalinity, which are added progressively until the desired alkalinity range is achieved. 

How to Increase Water Alkalinity

The following methods can be used to increase water alkalinity at home:

  • Baking soda: Adding ½ a teaspoon of baking soda to 1 gallon of water should alkalize the water to a suitable level. 
  • Fresh lemon: Lemon juice is acidic, but it has an alkaline effect when metabolized in the body. Use about 10 tablespoons of lemon juice per gallon of water. 
  • Alkaline booster drops: OTC pH booster drops are an easy way to increase alkalinity, as well. Make sure the drops are intended for use in drinking water, however.  

Industrial sites and water treatment facilities typically use an alkalinity-increasing product, such as soda ash or sodium hydroxide


Alkalinity is a measure of water’s ability to neutralize acids or resist changes that cause acidity, maintaining a stable pH. Titration is used to measure the alkalinity of a water sample, and water with a pH of 8 or higher is considered alkaline. Soils and geology have the biggest influence on water pH and alkalinity. There are numerous ways to increase water’s pH depending on the application and use point. 

About the Author

Brian Campbell

Brian Campbell is the founder of WaterFilterGuru.com, where he blogs about all things water quality. His passion for helping people get access to clean, safe water flows through the expert industry coverage he provides. Follow him on twitter @WF_Guru or contact him by email [email protected].

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